Chemical Process Design & Economics

7/21/2019 Chemical Process Design & Economics

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CHEMICAL PROCESS DESIGN AND ECONOMICS

Course Outline

CHAPTER ONE: Introduction: Methodology o The Design Process

1.1 Design

1.2 Fixed/regid Constraint1.3 The design process1.4 The design objective1.5 Data collection1.6 eneration o! possible design1." #election1.$ Che%ical &an'!act'ring (rocesses1.) Contin'o's and *atch (rocesses

CHAPTER T!O

2.1 Codes and #tandards

2.2 Design Factors

2.3 #+ste%s o! ,nits

2.4 &athe%atical -epresentation o! the Design (roble%

2.5 selection o! the Design ariables

CHAPTER THREE: OPTIMI"ATION

3.1 #i%ple &odels

3.2 &'ltiple ariable #+ste%s

3.2.1 &ethods o! nal+sis

3.2.2 #earch &ethods

3.2.3 0ther 0pti%iation &ethods

CHAPTER #O$R: %ATCH PROD$CTION PROCESS

CHAPTER #I&E: PROCESS S'NTHESIS

5.1 ntrod'ction5.2 -a &aterials and Che%ical -eactions5.3 e'ristics in 'ip%ent Design

CHAPTER SI(: PROCESS SIM$LATION

6.1 (rocess #i%'lator

CHAPTER SE&EN: PROCESS ECONOMICS

E(AMS

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There are to exa%s8

&id9se%ester and

Final exa%s.

GRADES

rades ill be assigned according to the !olloing distrib'tion8

&idter% 2:;

Final ":;

o%eor< proble%s 1:;

TE(T %OO)S

1. (lant Design and cono%ics !or Che%ical ngineers8 *+ (eters and Ti%%erha's

2. Co'lson = -ichardson>s Che%ical ngineering Design8 *+ #innot? ol'%e 6

CHAPTER ONE

INTROD$CTION: METHODOLOG' O# THE DESIGN PROCESS

*+* Design8 t is the s+nthesis o! ideas to achieve a desired goal @prod'ctA. The designer

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starts ith an idea and proceeds to develop several alternative designs that he eval'ates

and !inall+ settles on the one that satis!ies his objective @goalA.

The search !or alternatives8 this step beco%es necessar+ beca'se the designer ill be

constr,inedb+ several !actors.

*+- Constr,ints on , Design Pro.le/

1.2.1 Fixed/-igid Constraints8 these are constraints the designer %'st live ith o'tside

his in!l'ence. .g. ph+sical las? govern%ent reg'lations and standards. The !ixed

constraints de!ine the o'ter bo'ndar+ o! all possible designs.

1.2.2 Bess -igid Constraints8 these are constraints the designer can %anip'late inorder to

arrive at the best design. .g. %aterrials o! constr'ction? ti%e. These are interrnal

constraints over hich the designer has so%e control.

n s'%%arr+ e have the !olloing diagra%atic s


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#ig+ *+- The Design Constr,ints

The diagra% shos the design process as an iterative proced're beca'se as the design

proceeds the designer ill be loo


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e'ip%ent per!or%ances? ph+sical propert+ data. n large design co%panies? the+ have

in ho'se %an'als containing all the process


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#tage 28 Feed (reparation

#o%e p'ri!ication o! the ra %aterials ill be necessar+ to render the% in a !or%

re'ired !or !eed to the reaction stage.

#tage 38 -eactor

n the reactor the ra %aterials are bro'ght together 'nder conditions that pro%ote the

prod'ction o! the desired prod'ct. oever b+9prod'cts and 'nanted co%po'nds/

i%p'rities ill also be !or%ed.

#tage 48 (rod'ct #eparation

!ter the reactor? the prod'cts and b+9prod'cts are separated !ro% an+ 'nreacted %aterial.

! in s'!!icient 'antit+? the 'nreacted %aterial ill be rec+cled to either the reactor

directl+ or to the !eed p'ri!ication and preparation stage.

#tage 58 ('ri!ication

*e!ore sale? the %ain prod'ct is p'ri!ied to %eet prod'ct speci!ication. ! the b+9prod'ct

is also prod'ced in s'!!icientl+ large 'antities? it %'st also be p'ri!ied !or sale.

#tage 68 (rod'ct #torage

(rovision !or prod'ct pac


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1.).1 (lant attain%ent8 this is the percentage o! the available ho'rs in a +ear that the plant

operates. This is 's'all+ ):9)5;.

1.).2 Choice o! Contin'o's vers's *atch (rod'ction

The choice ill not be clear 9 c't? hoever one can 'se as a g'ide the !olloing r'les8

Contin'o's

1. (rod'ction rate greater than 5G1:6


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#ig+*+1 The structure o , che/ic,l engineering 9ro2ect

(hase 2. The detailed %echanical design o! e'ip%entH the str'ct'ral? civil and electrical

designH speci!ication and design o! ancillar+ services. 0ther specialist gro'ps ill be

responsible !or cost esti%ation? and the p'rchase and proc're%ent o! e'ip%ent and

%aterials.

The se'ence o! steps in the design? constr'ction and start 'p o! a che%ical process plant

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is shon diagra%%aticall+ in Fig.1.5.

.

#ig+*+4 Pro2ect Org,ni,tion

(roject %anagerH a che%ical engineer b+ training is responsible !or the coordination o!

the project.

CHAPTER T!O

-+* Codes ,nd St,nd,rds

The ter%s C0D and #TED-D are 'sed interchangeabl+? tho'gh C0D sho'ld be

reserved !or a code o! practices. That is a reco%%ended design or operating proced're.

#TED-D on the other hand re!ers to pre!erred sies? eg. pipes? co%position etc.

n %odern engineering practice e have standards and codes that cover vario's !'nctions

e.g

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1. &aterials? properties and co%position2. Testing proced'res !or per!or%ance? co%position and 'alit+3. (re!erred sies? eg t'bes? plates? sections4. Design %ethods? inspection? !abrication5. Codes o! practice? !or plant operation and sa!et+

ll developed co'ntries have national organiations responsible !or the iss'e and

%aintenance o! standards !or the %an'!act'ring ind'stries and !or the protection o!

cons'%ers.

n the ,.I8H *ritish #tandards nstit'tion

n the ,.#H Eational *'rea' o! #tandards

The+ are responsible !or coordinating in!or%ation on standards. #tandards are iss'ed b+

the Federal #tate and vario's co%%ercial organiations. The %ajor ones o! interest to

che%ical engineers are8%erican Eational #tandards nstit'te @E#A

%erican (etrole'% nstit'te @(A

%erican #ociet+ !or Testing &aterials @#T&A

%erican #ociet+ o! &echanical ngineers @#&A

nternational 0rganiation !or #tandardisation @#0A coordinates the p'blication o!

nternational #tandards.

n hana? there is no national standards organiation to coordinate local standards !or

ind'stries. oever there are national standard organiations ith standards !or the

protection o! cons'%ers eg. #tandards *oards? Food and Dr'g d%inistration @FDA?

and the nviron%ental (rotection genc+ @(A.

'ip%ent %an'!act'res or< together to prod'ce standardied designs and sie ranges

!or co%%onl+ 'sed ite%sH electric %otors? p'%ps? pipes? and pipe !ittings.

-+- #,ctors o S,ety ;Design #,ctors: He,t Tr,nser in re,ctors:to re%ove highl+ exother%ic heat o! reaction?

consider the 'se o! excess reactant? an inert dili'ent.

Heuristic **: For less exother%ic heat o! reaction? circ'late reactor !l'id to an external

cooler? or 'se a jac


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Heuristic *-: Pu/9ing ,nd Co/9ression: To increase the press're o! a strea%? p'%p a

li'id rather than co%press a gas8 i.e condense a vapor as long as re!rigeration @ and

co%pressionA is not needed be!ore p'%ping.

Co%pressors have large capital cost and cons'%e a lot o! poer.

#,&&-O 0F (-0C## D#E ,-#TC#

The disc'ssion !oc'sed on the !olloing8

9 'nderstanding the i%portance o! selecting reaction paths that do not involve toxic

or haardo's che%icals.9 *e able to distrib'te the che%icals in a process !losheet? to accont !or the

presence o! inert species? to p'rge species that o'ld otherise b'ild 'p to

'nacceptable concentrations? to achieve a high selectivit+ o! the desired prod'cts.9 ppl+ he'ristics in in selecting separation processes to separate li'ids? vapo'rs?

and vapo'r9li'id %ixt'res.9 ,nderstand the advantages o! p'%ping a li'id rather than co%pressing a vapor.

4+0 Heuristics in E?ui9/ent Design

5.3.1. 'ip%ent #ie

Eeed in!or%ation on the re'ired thro'ghp't to deter%ine vessel sie

9 eneral g'idelines !or vessel sieo eight8 291: %

o B/D8 295%

9 Toers/ Col'%nso eight8 295:%

o B/D8 293:%

Eote8 Do not speci!+ 'nits o'tside these ranges

5.3.2 eat xchangers

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#everal


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Eote that ? co%pressors are high cost ite%s8 large capital cost and high poer

cons'%ption

dvantages o! high press're

o #%aller vol'%es

o reater concentrationo Change ther%od+na%ics

Boer press'res processing conditions

o 191: bar is pre!erable

o igher press're or vac''% re'ires special e'ip%ent

o ,nless there is a co%pelling reason? operate at 191: bar press're

5.3.3.2 igh Te%perat're

0perate at high te%perat're to achieve the !olloing8

o igh reaction rates

o

Change e'ilibri'% o! reaction or B chieve a high te%perat're in a process b+ the !olloing %eans8

o F'rnaces@'sing !'el gas? oilA9 ver+ high te%perat'res

o eat exchangers@'sing stea%? ther%al !l'ids? %olten saltA

#tea%

o igh press're stea%8 4: 5:bar @approx. 26:oCA

o &edi'% press're stea%8 2: bar@approx. 2::oCA

o Bo press're stea%8 59 1: bar@approx. 15:oCA

5.3.3.3 Bo Te%perat're

0perate at lo te%perat're to achieve the !olloing8

o #lo reaction rate

o (revent ther%al sensitive species !ro% degradation

o Change ther%od+na%ics

chieve a high te%perat're in a process b+ the !olloing %eans8

o ,sing a heat exchanger ith the !olloing !l'ids@ cold stea%A

Cooling toer ater

Chilled ater

ctive re!rigeration

CHAPTER SI(: PROCESS SIM$LATION

9 (rocess si%'lation is the act o! representing so%e aspects o! the real orld b+

n'%bers or s+%bols that %a+ be easil+ %anip'lated to !acilitate their st'd+.9 The i%portant step in process si%'lation is the representation o! that aspect o! the

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real orld to be st'died in ter%s o! a %athe%atical %odel.9 Mith respect to che%ical engineering? the real orld is a che%ical process

described b+ a process !lo sheet. There!ore process si%'lation is 'sed to solve

proble%s related to the process !lo sheet? i.e process design? process anal+sis?

process control etc.9 The %athe%atical %odel that si%'lates an aspect o! the process needs an

appropriate %ethod o! sol'tion.9 process si%'lation is a co%p'ter progra% developed to solve the %odel and

st'd+ its behavior b+ %anip'lating the %odel para%eters.

5+* Process Si/ul,tor:

Co%p'tational pac


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6.1.2 ,nit 0perations #olversH e.g -eactors

9 speci!ies the reaction stiochio%etr+? te%perat're? press're and conversion

9 hen the reaction is e'ilibri'% li%ited? speci!ies the stoichio%etr+ ? the approach to

e'ilibri'% and e'ilibri'% constants

9 !or the reaction involved? speci!ies the


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CHAPTER SE&EN: PROCESS ECONOMICS

".: Cost sti%ation

n acceptable plant design %'st present a process that is capable o! operating 'nder

conditions hich ill +ield a pro!it. #ince net pro!it e'als total inco%e %in's all

expenses? it is essential that the che%ical engineer be aare o! the %an+ di!!erent t+pes

o! cost involved in %an'!act'ring process. C,9it,l %'st be allocated !or direct 9l,nt

e@9enses? s'ch as those !or ra %aterials? labor and e'ip%ent. *esides direct expenses?

%an+ other indirect e@9ensesare inc'rred and these %'st be incl'ded i! a co%plete

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anal+sis o! the total cost is to be obtained. xa%ples o! these indirect expenses are

ad%inistrative salaries? prod'ct9distrib'tion cost? and cost !or interplant co%%'nications.

capital invest%ent is re'ired !or an+ ind'strial process? and deter%ination o! the

necessar+ invest%ent is an i%portant part o! a plant9design project. The tot,l in3est/ent

!or an+ process consist o! i@edc,9it,l in3est/ent!or ph+sical e'ip%ent and !acilities

in the plant pl's =orBing c,9it,lhich %'st be available to pa+ salaries?


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The capital necessar+ !or the operation o! the plant

9 Total capital invest%ent J Fixed capital invest%ent L Mors !ees and contingencies. n %ost cases? constr'ction overhead is

proportioned beteen %an'!act'ring and non9%an'!act'ring !ixed9capital

invest%ent.

9 Mor


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co%panies. &ost che%ical plants 'se an initial ors !ees4. Contingencies

".4.1 T+pes o! capital cost esti%ates

n esti%ate o! the capital invest%ent !or a process %a+ var+ !ro% a predesign esti%ate

based on little in!or%ation except the sie o! the proposed project to a detailed esti%ate

prepared !ro% co%plete draings and speci!ications. The !olloing !ive categories

represent the acc'rac+ range and designation nor%all+ 'sed !or design p'rposes8

1. 0rder9o!9%agnit'de esti%ate@ration esti%ateA based on si%ilar previo's cost data8

probable acc'rac+ o! esti%ate over 30 percent2. #t'd+ esti%ate @!actored esti%ateA based on


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e'ip%entH probable acc'rac+ o! esti%ate 'p to 30 percent3. (reli%inar+ esti%ate @b'dget a'thoriation esti%ateH scope esti%ateA based on

s'!!icient data to per%it the esti%ate to be b'dgetedH probable acc'rac+ o!

esti%ate ithin 20 percent.

4. De!initive esti%ate@project control esti%ateA based on al%ost co%plete data b'tbe!ore co%pletion o! draings and speci!icationsH probable acc'rac+ o! esti%ate

ithin 10 percent5. Detailed esti%ate @contractor>s esti%ateA based on co%plete engineering

draings? speci!ications and site s'rve+sH probable acc'rac+ o! esti%ate ithin

5 percent.

".4.2. Cost ndexes

&ost cost data hich are available !or i%%ediate 'se in a preli%inar+ or predesign

esti%ate are based on conditions at so%e ti%e in the past. *eca'se prices %a+ change

considerabl+ ith ti%e d'e to changes in econo%ic conditions? so%e %ethods %'st

be 'sed !or 'pdating cost data applicable at a past date to costs that are representative

o! conditions at a later ti%e. This is done 'sing a cost index.

$ost indexis hence an index val'e !or a given point in ti%e shoing the cost at that

ti%e relative to a certain base ti%e.

=

obtainedas$ostorigina#timeatva#ueindex

timepresentatva#ueindex$ost+rigina#$ostesent(r

Cost indexes can be 'sed to give a general esti%ate? b't no index can ta


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index5

&ethods !or sti%ating Capital nvest%ent

@aA (oer !actor applied to plant9capacit+ ratio

@bA ,nit cost sti%ate@cA (ercentage o! delivered9e'ip%ent Cost@dA Bang !actors !or approxi%ation o! capital nvest%ent@eA Detailed te% sti%ate

Turno3er r,tios8 rapid eval'ation %ethod s'itable !or order9o!9%agnit'de

esti%ates is


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T+pes o! Depreciation

1. (h+sical depreciation8 is the %eas're o! the decrease in val'e d'e to changes in

the ph+sical aspect o! the propert+. Mear and tear? corrosion? accidents and

deterioration d'e to age.

2. F'nctional depreciation8 depreciation d'e to all other ca'ses. 0ne co%%on t+pe

o! !'nctional depreciation is obso#es$en$e. This is ca'sed b+ technological

advances or develop%ents that %a


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are8

1. *oo< val'e or 'na%ortied cost8 the di!!erence beteen the original cost o! a

propert+? and all the depreciation charges %ade to date.2. &ar


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the propert+ val'e at the beginning o! the partic'lar +ear. The !ixed percentage

!actor re%ains constant thro'gho't the entire service li!e o! the propert+? hile the

ann'al cost !or depreciation is di!!erent each +ear. ,nder these conditions? the

depreciation cost !or the !irst +ear o! the propert+>s li!e is !.

=herefre9resentsthe i@ed9ercent,ge ,ctor+t the end o! the !irst +ear?

A1@ fVVva#ue'sset a ==

t the end o! the second +ear?

2A1@ fVVva#ue'sset a ==

t the end o! the a+ear?

a

a fVVva#ue'sset A1@ ==

t the end o! the n+ear @ i.e. at the end o! service li!eA

sn

a VfVVva#ue'sset === A1@

There!ore?

ns

V

Vf

1

1

=

Pr,ctice uestion8 The original val'e o! a piece o! e'ip%ent is S22?:::?

co%pletel+ installed and read+ !or 'se. ts salvage val'e is esti%ated to be S2:::

at the end o! a service li!e esti%ated to be 1: +ears. Deter%ine the asset @ or boo


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necessar+ to


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E@,/9le:

ss'%e to e'all+ so'nd invest%ents Aand % co'ld be %ade.

nvest%ent A8 Capital neededJS1::?:::H (ro!it +ieldedJS1:?:::/+ear

nvest%ent %8 Capital neededJS1 %illionH (ro!it +ieldedJS25?:::/+ear

nvest%ent %gives a greater +earl+ pro!it than Ab't ann'al rate o! ret'rn on the second

invest%ent is onl+

@S25?:::/S1?:::? :::A x1::J2.5;

Mhile ann'al rate o! ret'rn on S1::?::: is 1:;.

*eca'se reliable bonds and other conservative invest%ents o'ld +ield ann'al rates o!

ret'rn in the range o! 6 to );? the S1 %illion invest%ent in this exa%ple o'ld not be

ver+ attractiveH the 1:; ret'rn on the S1::?:::capital o'ld %a


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capital

To deter%ine pro!itH esti%ates %'st be %ade o! direct prod'ction cost?

!ixed charges incl'ding depreciation? plant overhead costs? general

expenses

(ro!its %a+ be expressed on a be!ore9tax or a!ter9tax basis b't the

condition %'st be indicated.

E@,/9le:

proposed %an'!act'ring plant re'ires an initial !ixed capital invest%ent o!

S)::?::: and S1::?::: o! or


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necessar+ to recover the original capital invest%ent in the !or% o! cash !lo to the

project based on total inco%e %in's all costs except depreciation. enerall+ !or

this %ethod? original capital invest%ent %eans onl+ the original? depreciable?

!ixed9capital invest%ent? and interest e!!ects are neglected. Th's

on7rdepre$iatiavgprofit7ravg

investment$apita#fixededepre$iab#earsinperiodaout

+

=

Chemical Process Design & Economics

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