Plant design

Plant design

1. AssocProf DrRashmi Walvekar (CEng, IChemE, UK)
ROOM:A4#450
EMAIL:[email protected]
CME 322
PLANT EQUIPMENT
DESIGN

2. TEACHING METHOD ANDASSESSMENT
✓Lecture: 15weeks
✓Tutorial: 10 weeks (Week4-13)
✓ContinuousAssessments
▪Group Assignment50%
✓Final examination50%
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DOCUMENTS
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3. COURSE LEARNING OUTCOME
(CLO)
CLO 1:Demonstrate mastery
of the design method and
design specification of
chemical equipment
andtheir parts.
CLO 2: Apply methods of
stress analysis and
calculations to ascertain
conformity to standardsof
chemicalindustry.
CLO 3: Demonstrate
knowledge and skills to
solve problem of
chemicalequipment
designs.

4. TEXTBOOK

5. INTRODUCTION TODESIGN
LECTURE 1

6. At the end of this lecture, students will be able to
-Understand basis of process synthesis and design
-Analysethe process synthesis routes using THREE different approaches
-Understand the importance of engineering materials and their selection
criteria.

7. PROCESS SYNTHESIS AND DESIGN
A process design establish the sequence of
chemical and physical operations.
Operating conditions, duties, major
specifications, material of construction (for
all process equipment)
General arrangement of equipment to
ensure proper functioning of plant (line
size, process controls and instrumentation)
Mass and energy balances and individual
equipment specification
Process
optimization
Preliminary
design
Cost
estimation
Plant
expansion

8. PROCESS SYNTHESIS AND DESIGN
PROCESS
Operations?
Connectivity?
Conditions?
Available
feedstock
Desired
product
Choosing a combination of operations, connectivity and conditions to
transform feedstock to desired product

9. Process synthesis and design
PROCESS
Operations?
Connectivity?
Conditions?
Available
feedstock
Desired
product
Why is it difficult??
•A large number of operations
• Many ways to connect units
• An infinite choice of operating conditions and equipment
design parameters
→We cannot try every possibility, or even come close to it

10. ANATOMYOFCHEMICALPROCESS
Ref: Sinnot andTowler, 2019

11. THREE BROAD APPROACHES TO PROCESS SYNTHESIS
1. Modify an existing
structure
‘Take an existing
process and tweak it’
2. Sequentially build
up a new structure
‘Divide and conquer:
build up the structure
in a series of logical
steps’
3. Superstructure
optimisation
‘Take a very flexible
structure with in-built
redundancy and
simplify it’

12. Approach 1: Synthesis by modifying an existing structure
─Add, delete or modify units to
suit the desired product,
available feed or other
conditions (cost of energy,
water, …)
─it is not really new synthesis
─Advantages
■Quick way to start
■Uses a proven process (and
probably one approved by
regulators)
─Disadvantages
■Suppresses innovation
■Flowsheet may be good for its
original design conditions, but
may not be best for the current
conditions of interest

13. APPROACH 2:Synthesis By Sequentially Building Up A New Structure
Relies on considering the process as a hierarchy of operations, then
building up the structure in a series of steps according to the
hierarchy
Several synthesis “models” for processes are available (Smith and Douglas)
●At each step, make decisions based on the information available at that
stage, that is, it is a sequence of ‘best local decisions’
●Decisions are based on heuristics or algorithmic methods
●Equipment is added to the flowsheet only if it can be technically and
economically justified
●Consequently, the structure developed is irreducible, meaning that it
contains no redundancy(compare with approach 3.)
(Smith, p11)

14. The synthesis tree concept

15. Smith -Onion model for Plant Design

16. Douglas –Process synthesis decision hierarchy
Decision Hierarchy
Level 1: Batch v continuous (Start here)
Level 2: Input-output structure of the flowsheet
Level 3: Recycle structure and reactor considerations
Level 4: Separation system specification
Level 4a: Vapour recovery system
Level 4b: Liquid recovery system
Level 5: Heat exchanger network (Finish here)
Economic evaluationis
usedatendofeachlevelto
findfeasiblerangeof
designvariablesandto
decidewhethertocontinue
withthedesign

17. ●ADVANTAGES
─The design team is in control at each stage of the process, and can gain a
feeling for the issues
─Concerns such as safety and plant layout can be included in the decision
making process as the design proceeds
●DISADVANTAGES
─At each stage, the best option is sought, but it may not be possible to decide
which is best without evaluating competing options
–consequently many designs must be completed and optimized
─There is no guarantee that the optimum design is chosen because it is not
possible to evaluate every option
─Complex interactions between different parts of the flowsheet may not be
recognized and exploited
APPROACH 2:Synthesis By Sequentially Building Up A New Structure

18. APPROACH 3:Synthesis By Superstructure Optimisation
Asuperstructureisaflowsheetthatcontainsallfeasibleunit
operationswithallfeasibleinterconnections(forthedesignproblem
underconsideration)
●Thesuperstructureisareducibleflowsheetthatintentionally
containsredundancy
●Itisintendedthattheoptimalstructureisembeddedsomewhere
withinthesuperstructure
●Optimisationisappliedtothesuperstructuretorevealthebest
structureandparametervaluessimultaneously
●Comparedtoapproach2,asequenceofdiscretedecisionmaking
stepsisreplacedbyamixedstructureandparameteroptimisation
problem
(Smith, p11)

19. Superstructure optimization of the olefin separation process
•DOI:10.1016/S1570-7946(03)80113-X

20. ●ADVANTAGES
─Many different design options are considered simultaneously, compared to
sequentially with approach 2.
─Complex interactions and tradeoffs in the plant are considered automatically
─Consequently, the design process can be automated and, once set up, can
produce designs quickly and efficiently
●DISADVANTAGES
─It can’t reach the best solution if the optimal structure is not embedded
somewhere in the superstructure
─Mixed discrete/continuous optimisationscan be large and difficult problems to
solve
─Most serious problem –the design team is removed from the decision making
process; building up process understanding is lost; and it is difficult to include
factors such as safety and layoutin the formulation of the optimisation problem
Approach 3:Synthesis by superstructure optimisation

21. SUMMARY OF DESIGNPROCESS
Ref: Sinnot andTowler, 2019
Tools used to aid process synthesis
●Heuristics(rules of thumb)
●Algorithmic methods -systematic
approaches (Used after a synthesis tree
has been created) -LINGO
●Process simulation (such as HYSYS,
SysCAD, Unisimand Aspen Plus)

22. ▪The design process
Determine
customer needs
Set design
specifications
Generate
design
concepts
Evaluate
Economics,
Optimize &
Select Design
Detailed
Design &
Equipment
Selection
Build
Performance
Models
Predict Fitness
for Service
Procurement &
Construction
R&D if Needed
Begin Operation
Customer
Approval

23. DESIGNCONSTRAINTS
Resources
Government controls
Choice of process
Process conditions
PLAUSIBLE
DESIGNS
External
Constraints
Internal Constraints
External constraints are outside designers
influence
Internal constraints can be controlled by
designer
KEY:meet the
design objective

24. MATERIALS OF CONSTRUCTION
1.INTRODUCTION
Ref: Chapter 7
Sinnotand Towler

25. MATERIALOFCONSTRUCTION
ENGINEERINGMATERIALS
Themostimportantcharacteristicstobeconsideredwhenselectinga
material of constructionare:
1. Mechanicalproperties
(a) Strength -tensilestrength
(b) Stiffness -elastic modulus (Young’smodulus)
(c) Toughness -fractureresistance
(d) Hardness -wearresistance
(e) Fatigueresistance
(f) Creepresistance

26. 2.Theeffectofhighandlowtemperaturesonthemechanicalproperties
3.Corrosionresistance
4.Anyspecialpropertiesrequired
(a)thermalconductivity
(b)electrical resistance
(c)magneticproperties
5. Easeoffabrication-forming,welding,casting
6. Availabilityinstandardsizesplates,sections,tubes
7. Cost

27. MATERIALOFCONSTRUCTION.
ENGINEERINGMATERIALS
5categories
✓Metals
✓Ceramics andglasses
✓Polymers
✓Composites
✓Semiconductors

28. ENGINEERINGMATERIALS
Metals
The most typical engineering material:
structuralsteel(analloyofcarbonandiron)
Metalliccharacteristics:
1.Strong: canwithstand high impact
loading withoutfracture
2.Ductile: readily formed into practical
shapes,permitsmallamountsofyielding
tosuddenandsevereloads
3.Goodconductor:Heatandelectric
current

29. ENGINEERINGMATERIALS
EXAMPLE:

30. ENGINEERINGMATERIALS
Ceramics
•Madeupofatleastonemetallic
elementandoneofthefivenon-
metallicelements(C,N,O,PorS)
•Asopposedtometals,theyarebrittle
•Examples: aluminium oxide (Al2O3),
magnesium oxide (MgO), silica(SiO2),
silicon nitride (Si3N4), aluminium
silicate (Al2SiO5), silicon carbide(SiC)

31. ENGINEERINGMATERIALS
Ceramics
1. Aluminium oxide(Al2O3)
•Chemically stable in a wide
variety of severe environments
whereas metallic aluminiumwill
oxidizeeasily.
•Higher melting point(2020
oC)
than aluminium (660
oC)

32. ENGINEERING
MATERIALS
Ceramics
2. Silicon nitride(Si3N4)
•Greater strength andhigher
resistant tofracture.
•Primary candidate for high-
temperature,energy-efficient
automobileengines

33. ENGINEERINGMATERIALS
Glasses
•As opposed to ceramics,
glasses arenon-crystalline
•Usually 72 wt% SiO2 with the
balancebeingNa2OandCaO
•Brittle
•Chemically-inert
•Transparent (visible,ultraviolet,
infraredradiation)

34. ENGINEERINGMATERIALS
Glass-ceramics
•Example: Lithiumaluminosilicate
•Convert from glassy (non-crystalline) to
ceramic(crystalline)statethroughheat
treatment
•Superior mechanicalstrength
•Low thermal expansioncoefficient
•Resistanttofractureduetosudden
temperaturechange
•Suitable forcookware

35. ENGINEERINGMATERIALS
Polymers(plastics)
•Organicchemistry
•Long-chain molecules composedof
many monomers bondedtogether
•Elements involved: C,H, O, N, F, Si
•Example: polyethylene (??????2??????4)??????, wheren
ranges from 100 to1000
•Others: acrylic, fluoroplastics(Teflon),
nylon,silicones
Columnprotector

36. Step1:Decideonthegeneraltypeofmaterial
Step2:Decideonthespecificmaterialwithinthatcategory
✓Metals,ceramicsandpolymersarecommonstructuralmaterials.
✓Compositesarecommonlyusedforspecialapplications.
✓Semiconductorsareusedforelectronicdevices.
SELECTION OFMATERIALS

37. Theselectionofmaterialsofconstructionforprocessequipmentand
pipingdesigninvolvemanyfactors.
a) Designobjective
Differentfieldhasdifferentdesignfocus.
1. Chemicalengineer
-theabilityofthematerialtoresistcorrosionundertheprocessconditions.
2. Mechanicalengineer
-strength andworkability
SELECTION OFMATERIALS

38. b) Temperature
Theeffectoftemperatureonmechanicalproperties.
Tensilestrengthandelasticmodulusofcarbonsteeldecreasewithincreasing
temperature.
Temperature(oC) 25 500
Tensile strength(N/mm
2
) 450 210
Young’s modulus(kN/mm
2
) 200 150
SELECTION OFMATERIALS

39. Economics
-Totalcostoffabricatedequipmentandpiping:
✓Total installationcost
✓Servicelife
✓Maintenancecosts:amountandtiming
✓Replacementcosts:amountandtiming
✓Costofdowntime(for maintenanceandreplacement)
SELECTION OFMATERIALS

40. MATERIALS STANDARDS AND
SPECIFICATIONS
✓AmericanNational Standards Institute (ANSI) –piping codes
✓AmericanSocietyofMechanicalEngineers(ASME)–boilerandpressure
vesselcodes
✓AmericanSocietyforTestingandMaterials(ASTM)
✓International Organization for Standardization(ISO)

41. Advantages:
✓Asameasureofinterchangeabilitybetweendifferentmanufacturers.
✓Mass production: Reducedmanufacturing costs
✓Facilitatethedesignstageasthedimensionisknown.
✓Facilitatemaintenanceaspartsareinterchangeableeasily.
MATERIALS STANDARDS AND
SPECIFICATIONS

42. Examples
ASTM A414 –Grade G(low-alloy steel)
-Iron + 0.31 wt% C (max) + 1.35 wt% Mn (max) + 0.035 wt% P
(max) + 0.04 wt% S(max)
MATERIALS STANDARDS AND
SPECIFICATIONS

43. HOMEWORK
1.SearchONEchemicalprocessequipmentthatisdesignedfromanyof
engineeringmateriallearnedtoday.Stateatleastonereference.
2.Preparea1slide onyourfindinganddiscuss during tutorial class (week 4)
a)Introduction–nameofequipment,picture/diagram,thedesign
materialproperties,operatingconditions(ifany).
b)Why that material is specifically selected for that equipment in chemical
process
c)References
3.ReferencemustbefromscientificjournalsONLY.
4.Each studentwilldopresentationintutorialclassin 3 min.

44. THANK YOU