Individual Design Studies

7/27/2019 Individual Design Studies

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Design Project 499

Process Design Project 599



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Nature of design work Key documents

Common uncertainties◦ Design methodology

◦ Safety factor

◦ Critical review

Characteristics of better and poorer design

studies





•

E.g. relationship betweenfactors in distillationcolumn design

• Geometry Operation

• In this unit we’ll distinguishbetween three facets

• Process design

• Operational design

• Mechanical design

• See also Martyn Ray’s viewof design on Blackboard

and the handout from R&S

(Woods, p92-93)



Memo 1

Volume 1

Memo 2

Memo 3

Volume 2

...

Sets the conditionsand specificationsfor the individualdesigns in Vol 2

Major A

Minor A

Major B

Minor B

Major C

Corrected,revised,expandedbecome

In general, don’trevise Vol 1 based on

the results of Vol 2(but discuss potentialeffects in the Vol 2critical reviews)









Methodology is the overall approach taken to perform the designwork, expressed as a series of steps◦ Actual equations are not usually mentioned◦ Rather: “Calculate X”, “Decide Y”, “Check Z”, ...

Simple distillation columns, heat exchangers, … have readilyavailable and well-established design methodologies, e.g.◦ Distillation columns: T&S, Ch11; Ludwig, Vol2; GPSA, Sec19◦ Heat exchangers: T&S, Ch12; Ludwig, Vol3; GPSA, Sec8–11

Some aspects of design are covered by Codes and Standards,e.g.◦ AS1210: Australian Standard for Pressure Vessels – covering mechanical

design of unfired vessels and their supports, manufacture, testing, safetysystems

◦ AS4041: Australian Standard for Pressure Piping – covering mechanicaldesign of process piping, manufacture, testing, safety systems



(T&S, p845)





The library is your friend◦ Catalogue(s), databases, interlibrary loans (?), document delivery (??), … + Perry’s

Try to get drawings or photos of the equipment◦ Old books, Google images, manufacturer’s brochures, journals perhaps, …

Ask your industry / academic advisor + look at the R&S handout

What are the key issues and main phenomena involved?◦ Tease them apart then think how they are connected…

Go back to the fundamentals: mass and energy balances, rate equations

Don’t wait, make a start!

If some data are very uncertain, pick a value and check sensitivities

If you don’t have much depth in one area of your design, then focus onanother… but get confirmation with your academic advisor





An amount of “overdesign” / “over-sizing” to allow for◦ Uncertainties in design methods◦ Uncertainties in design data◦ Need for operation above nominal specs (“nominal” = the flows

and conditions in your stream tables)

A balance between◦ Making the equipment a bit bigger to be sure it can handle therequired duty

◦ Making the equipment so big that it becomes too costly

Can be implemented in several ways, e.g.◦ Increase the unit’s feed stream flowrate(s) by x%◦ Increase performance specifications by y%◦ Reduce the efficiency / increase area / increase number of trays /

… by z%

Ask your industry / academic advisor

(P&T, p81-84; T&S, p17-18; Hills, Ch4)



The safety factor (and its implementation) must beclearly reported

Should check that operation at the nominal flowrateis acceptable, e.g.◦ Nominal heat exchanger flow is 30 kg/s for one stream◦ Use design factor of 10% on the flowrate design the HX

for a flow of 33 kg/s

◦ But, in normal operation the flow will be only 30 kg/s◦ This means the operating OHTC will be lower than design

conditions (since lower v

lower h and higher Rfouling)◦ Will the HX still work with a lower OHTC? Need to check!

Can be 0%, but 10% is typical (and see next slide)

(P&T, p81-84; T&S, p17-18; Hills, Ch4)



(P&T, p82)





It’s a self-critique of your design work and decisions

It is not a summary of the design produced ( 0/10)

Needed in both major and minor individual design studies

It’s an instance of “reflective practice”, which is valued byEngineers Australia

What one student said:◦ “Taking a step back and reflecting on the project was an

unfamiliar experience. For the major design project my state of

mind has been ‘down and in the trenches’ focusing on what needsto be done next with no self-reflection. Analysing my work with aself-critique point of view was fairly engaging, I learnt a lot aboutmyself and my approach to problem solving…”



Re-evaluate your assumptions

Discuss the limitations of the design methods used

Discuss how uncertainties were handled

Compare your design with designs in the literature

Discuss your reservations about the work and also your reasons forhaving confidence in it

Outline any experimental work or further simulation work that should beperformed

Discuss what you would do differently if you had to do it again

Discuss optimisation possibilities

Reflect on the most important issues or key parameters uncovered indesigning that type of unit



What were the good points of your design work? What are thegood features of your approach you want to tell people about?

What parts need more attention? What are your reservations about the design you’ve come up with?

What extra information would you have liked? How exactly would

you have made use of it? How did you cope with not having allthe information you wanted?

Did you find anything unexpected?

Did you use any innovative design methods or technology? Didyou do some extra work that most other people did not?

Your final design might be different and perform differently fromthe equipment envisaged in Volume 1. How would thesedifferences affect the rest of the process?



T h e r m o d y n a m i c s

( V L E m e t h o d , …

)

R e a c t i o n s

( s p e c i e s ,

s t o i c h i o m e t r y ,

e q u i l i b r i a ,

k i n e t i c s , …

)

H y d r o d y n a m i c s

( w e l l m i x e d , p l u g

f l o w , …

)

H e a t t r a n s f e r

( m o d e , r a t e

e q u a t i o n ,

l o s s e s ,

… )

M a s s t r a n s f e r

( d r i v i n g f o r c e ,

i n t e r f a c i a l a r e a ,

… )

P e r i p h e r a l s

( p u m p s , p i p e s ,

t a n k s , …

)

I n t e r a c t i o n s

w i t h r e s t o f p l a n t

( u p s t r e a m ,

d o w n s t r e a m )

E t c .

Assumptions, approx-

imations, limitations inmethods used

Alternative approaches

Accuracy of data, andits implications,sensitivities

Time scales (short,long), dynamics, start-up / shutdown

Key issues uncovered,unexpected items

Recommendations

Etc.





Poorer designs

◦ Forget to mention these things

◦ Focus on mechanical designbecause there are lots of

equations◦ Seem to be mostly qualitative

◦ Ignore the vessel’s pipes,pumps, …

◦ Are presented “as is”

◦

Documents look “homemade”,as if the designer had not seenexamples before

◦ Leave out the critical review orwrite it as a summary

Better designs

◦ Have clear scope, designrequirements, methodology

◦ Focus on process andoperational design

◦ Are strongly quantitative

◦ Include peripherals

◦ Show evidence of checking

◦

Have professional lookingequipment spec sheets,mechanical drawings, …

◦ Have a thoughtful criticalreview





The major and minor studies need to be decided uponand stated in Memo 3◦ In consultation with fellow group members and your academic

(and possibly industry) advisor

Work on your major and minor studies in parallel◦

Keep Volume 1 revisions ticking over as well Don’t spend forever trying to get that last piece of data:

pick a value and proceed

Look carefully at the scope of work to make sure youdon’t leave anything out

Keep in contact with your academic and industryadvisors – you don’t just need them in Weeks 1–6



GPSA: Gas Processors Suppliers Association (2004) Engineering Data Book, 12ed, Gas Processors Suppliers Association, Tulsa, OK Ludwig: EE Ludwig (2007) Applied Process Design for Chemical and

Petrochemical Plants , 3ed, Gulf Professional Publishing, Houston, TX Perry: RH Perry and DW Green (eds) (2008) Perry's Chemical Engineers’

Handbook , 8ed, McGraw-Hill, New York P&T: MS Peters, KD Timmerhaus and RE West (2003) Plant Design and

Economics for Chemical Engineers, 5 ed, McGraw-Hill, New York R&S: MS Ray and MG Sneesby (1998) Chemical Engineering Design

Project: A Case Study Approach, 2ed, Gordon and Breach SciencePublishers, Amsterdam

T&S: G Towler and R Sinnott (2008) Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design, Butterworth-Heinemann, Burlington, MA

Woods: DR Woods (2007) Rules of Thumb in Engineering Practice, Wiley-VCH, Weinheim, Germany