Concise Guide to Heat Exchanger Network Design: A Problem-based Test Prep for Students

154 Pages·2021·7.051 MB·English

by  Xian Wen Ng

Xian Wen Ng
Concise
Guide to Heat
Exchanger
Network Design
A Problem-based Test Prep for Students
Concise Guide to Heat Exchanger Network Design
Xian Wen Ng
Concise Guide to Heat
Exchanger Network Design
A Problem-based Test Prep for Students
XianWenNg
Singapore,Singapore
ISBN978-3-030-53497-4 ISBN978-3-030-53498-1 (eBook)
https://doi.org/10.1007/978-3-030-53498-1
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Preface
Thermalenergyisoneofthemostimportantsourcesofenergydrivingprocessesin
industrial plants, and one of the key engineering outcomes is often effective heat
integrationandenergyrecoverybetweenprocessstreams.Itiscriticalforengineers
and related professionals to master the technique of designing optimal heat
exchanger networks that achieve maximum energy conservation, while not
compromisingondesiredproductionobjectives.
This pocket guide serves as a supplementary learning resource that will help
studentsdeconstructsomeofthemostchallengingproblemsencounteredinthetopic
of Heat Exchanger Networks. The practice problems in this book were carefully
selected to represent the most commonly encountered problems found in tests and
examinations. Withthecomprehensiveworkedsolutionsanddetailedexplanations
provided for each problem, students will be able to closely follow the thought
processofproblem-solvingfromstarttofinish,therebyhonetheirskillsinapplying
abstracttheoreticalconceptstosolvingpracticalproblemswhichiscriticalforacing
examinations.
Themixofbothnumerical andopen-endedproblemsincludedinthisbookwill
help students gain a well-roundedunderstanding ofHeat Exchanger Networks and
related design principles. With the use of this study guide, students will become
proficientnotonlyinhandlingnumericalanalysisbutalsoinrelatingthesignificance
ofdesktopproblem-solvingtothelargerreal-worldcontext.
Singapore,Singapore XianWenNg
v
Acknowledgements
MyheartfeltgratitudegoestotheteamatSpringerfortheirunrelentingsupportand
professionalismthroughoutthepublicationprocess.SpecialthankstoMichaelLuby,
Brian Halm, and Hema for their constant effort and attention towards making this
publication possible. I am also deeply appreciative of the reviewers of my manu-
scriptwhohadprovidedexcellentfeedbackandnumerousenlighteningsuggestions
tohelpimprovethebook’scontents.
Finally,Iwishtothankmylovedoneswhohave,asalways,offeredonlypatience
andunderstandingthroughouttheprocessofmakingthisbookareality.
vii
Contents
1 FundamentalsofHeatIntegration. . .. . . . . . .. . . . . . . .. . . . . . . .. 1
2 EnergyCascadeandPinchAnalysis. . . . . . . . . . . . . . . . . . . . . . . . . 19
3 Euler’sTheoremandGrandCompositeCurves. . . . . . . . . . . . . . . . 63
4 ComplexHenDesignProblems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
ix
About the Author
Xian Wen Ng graduated with First-Class Honors from the University of Cam-
bridge,UK,withaMaster’sDegreeinChemicalEngineeringandBachelorofArts
in2011andwassubsequentlyconferredaMasterofArtsin2014.Shewasranked
second in her graduating class and was the recipient of a series of college scholar-
shipsincludingtheSamuelTaylorMarshallMemorialScholarship,ThomasIreland
Scholarship, and British Petroleum Prize in Chemical Engineering for top perfor-
manceinconsecutiveyearsofacademicexaminations.Shewasalsooneofthetwo
students from Cambridge University selected for the Cambridge-Massachusetts
Institute of Technology (MIT) exchange program in Chemical Engineering, which
shecompletedwithHonorswithacumulativeGPAof4.8(5.0).Duringhertimeat
MIT, she was also a part-time tutor for junior classes in engineering and pursued
otherdisciplinesincludingeconomics,realestatedevelopment,andfinanceatMIT
and the John F. Kennedy School of Government, Harvard University. Upon grad-
uation,shewaselectedbyhercollegefellowshiptothetitleofscholar,asamarkof
heracademicdistinction.
Since graduation, she has been keenly involved in teaching across various
academiclevels.Hertopicsofspecializationrangefromsecondary-levelmathemat-
ics, physics, and chemistry up to tertiary-level mathematics and engineering sub-
jects. Some of her recent publications include Engineering Problems for
Undergraduate Students and Pocket Guide to Rheology, which are practice books
similarlywrittenforstudentstakingengineeringandrelatedSTEMcoursesathigher
education and university levels. These books aim to sharpen students’ problem-
solvingskillsandputthemingoodsteadfortestsandexaminations.
xi
Chapter 1
Fundamentals of Heat Integration
Problem1
Consider an industrial process that comprises three process streams as tabu-
latedbelow.Determineiftheoverallsystemisanetheatsourceorheatsink.
Process Supplytemperature, Targettemperature, Flowrateheatcapacity,
(cid:1) (cid:1)
stream T [C] T [C] W[kW/K]
supply target
1 200 70 0.4
2 100 170 0.7
3 80 150 1.0
Solution1
ClassifyingProcessStreams—HotandColdStreams
Before we begin, we should first identify the nature of the process streams in
termsofwhethertheyare“hot”or“cold”streams.Thisisakeystepintacklingheat
exchangernetworkproblems,especiallysowhenproblemsgetmorecomplex.
Fromthetablegiven,wenotethatoneofthestreamsishotwhiletheothertwoare
cold streams. The hot stream needs to be cooled down to a prescribed target
temperature, while the cold streams need to be heated to their target temperatures,
inordertomeetrequiredprocessingconditions.
Process Hot or Supply Temperature, Target Temperature, Flow rate heat
Stream cold? [℃] [℃] capacity, [ / ]
1 Hot 200 70 0.4
2 Cold 100 170 0.7
3 Cold 80 150 1.0
©TheEditor(s)(ifapplicable)andTheAuthor(s),underexclusivelicenseto 1
SpringerNatureSwitzerlandAG2021
X.W.Ng,ConciseGuidetoHeatExchangerNetworkDesign,
https://doi.org/10.1007/978-3-030-53498-1_1
2 1 FundamentalsofHeatIntegration
Note also that “flow rate heat capacity” denoted as W is simply heat capacity
applied to continuous flows such as process streams in steady-state operations.
Mathematically, it is the product of heat capacity and flow rate as shown below,
wherebyWattisequivalenttoJoulespersecond.
(cid:1) (cid:3)
kJ
Flow rate heat capacity½kW=K(cid:3)¼Flow rate½kg=s(cid:3)(cid:4)Heat capacity
kg∙K
TotalHeating(orCooling)Requirement
Inthissimpleexample,wecancalculatetheheating(orcooling)requirementfor
theentire process (i.e., heatingand cooling duties required) inorder toachievethe
desiredtargettemperaturesoftheprocessstreams.
Thetotalrequiredcoolingdutyforthehotstream1canbedeterminedasfollows:
(cid:4) (cid:5)
Q ¼ T (cid:5)T (cid:4)W ¼ð200(cid:5)70Þ(cid:4)0:4¼52kW
c supply target 1
The total required heating duties for cold streams 2 and 3 can be determined as
follows:
(cid:4) (cid:5)
Q ¼ T (cid:5)T (cid:4)W ¼ð170(cid:5)100Þ(cid:4)0:7¼49kW
H,2 target supply 2
(cid:4) (cid:5)
Q ¼ T (cid:5)T (cid:4)W ¼ð150(cid:5)80Þ(cid:4)1:0¼70kW
H,3 target supply 3
Q ¼Q þQ ¼49þ70¼119kW
H H,2 H,3
Thenetheatingrequirementisthereforethesumofallheatingandcoolingneeds
as computed below. Assuming we define Q > 0 as a system that requires input of
heat,thenweaddanegativesigntothecoolingdutyandarriveatthefollowing.
Q¼(cid:5)Q þQ ¼(cid:5)52þ119¼67kW
c H
This shows that the overall system requires a heating duty of 67 kW, and it is
thereforealsoanetheatsink(systemneedsto“takein”heatandthesupplyofthis
heatisdonethroughtheheatexchangerwhichprovidestheheatingdutyof67kW).
Problem2
Discuss the concept of heat integration in relation to the heating (or cooling)
requirementsinatypicalprocessplant.Consideranybenefitsandtrade-offsof
heat integration and explain how heat exchangers may help achieve heat
integration.
Solution2
WhytheNeedforHeatIntegration?
Heat energy is an indispensable source of energy driving many industrial pro-
cesses, thereby ensuring the optimal use of heat through energy conservation and