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CHAPTER 1Introduchon

The Role of the Chemical Engineer

The chemical engineer is one who is skilled in development, design,construction, and operation of industrial plants in which matter under!goes a change" Chemical engineers work in four main divisions of thechemical process industries# research and development, design, manu!facturing, and sales" This is illustrated in the frontispiece of this $ook"

The chemical engineer prospers $ecause he is versatile% he is well groundedin the fundamental sciences of chemistr&, ph&sics, and mathematics, &etknows 'when to appl& empirical engineering know!how to solve pro$lems"

The decisions which make progress possi$le in engineering (develop!ment, design, construction, operation, or management) from an economicnecessit& are $ased on inade*uate data $acked up $& e+perience andsound udgment" -uch decisions represent the highest form of e+pression

of engineering" In this manner, the engineer soives the pro$lems vrhichhave to $e solved"

Chemical Engineering Design

Chemical engineering design consists of process, e*uipment, and $uild.ing designs for manufacturing plants to suppl& the product needs of thecustomers" /ore and more, the creative function e+empli0ed in designhas $ecome a determining characteristic of the chemical engineer" -incechemical engineering design is a fundamental chemical engineering pro$!lem, it is essential that the chemical engineer should recognie designas his responsi$ilit& in connection urith chemical industries"

2esign should follow some prearranged plan $ased upon space re*uire!ments, selections and speci0cations of process e*uipment, the la&out ofprocess e*uipment according to processing 34ovs, plant location, plantsite selection, and future e+pansion" 5oth $uilding and e*uipmentshould $e designed to give the most e6cient production 7vith a minimumof handling of material in process" Provision should $e made for storage,for e+pansion to 0t in with the original arrangement without distur$ingthe 8ow of work, and for the most favora$le and economical conditionsof operation of each piece of e*uipment with respect to all varia$les"2esign is Centered a$out pro$lems of rates of mass and energ& transferand of chemical change" . 9ther factors that should $e considered in the

design of $uilding and e*uipment arrangement include possi$le haardsof 0re, e+plosion, chemical inur&, and inur& to health, the welfare of the+voricer, economical distri$ution of process steam and power, and e+pan!sion of production"All other factors $eing e*ual, intelligent and careful design has ever&advantage over one that has grown up or $een put together in a hit!or!miss fashion $& alterations, hunches, and additions" The task of thechemical engineer is to calculate *unntities and &ields, to consider thehandling of materials in process and in storage, to appl& technicalknowledge of material and energ& $aiances, mass and heat transfer $&convection, di8usion, and conduction, the 4ow of 0uids, the separation ofmaterials, the thermod&namics and e*uili$ria of reacting s&stems, the

$ehavior of catal&sts, and the kinetics of all t&pes of chemical reactions"In addition, the engineer must develop detailed costs of each unit opera.tion so that even $efore the plant is in the $lueprint stage, he will know

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not onl& the cost per ton for processing the raw materiais, $ut also thecost per unit +veight of material in each operation, such as grinding,cr&stalliation, 0ltration, evaporation, dr&ing, etc"

Need for Plant Design

The main factor which dictates the decision to produce a new productor e+pand or modernie present facilities is generall& an economic one asrepresented $& the *uestion ':hat will $e the return on the investment;) $& improving or replacing products urhich, $ecause ofmarket saturation, have shown declining pro0ts, and (@) $& advancing$&!product or waste products to a pro0ta$le status"

Items such as market opportunities, competition, and distri$ution arestudied $& the market anal&sts" Production and economic aspects of!

product design confront the design engineer 7vith these t&pical *uestions ?Production1" Is the product properl& designed from a cost and productionviewpoint;=" Can a necessar& new process $e integrated with e+isting plantfacilities;>" :hat is the $est process for producing the product;@" :hat new e*uipment is needed;" How much plant space is needed;B" Can the product $e rnanufactured e0icientl&;

" :hat is the status of raw materials; -hould an& of these $e

manufactured;

Economics

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1" :hat is the estimated manufacturing cost per unit;

=" 7Dhat is the estimated sales and advertising e+pens per unit;

>" How much capital is re*uired;

@" How much inventor& is needed;

" Can a *ualit& product $e produced at a price consumers will pa&;B" How long 7rill it take the product to reach a $reak!even $asis;

" :hat is the long!term pro0t outlook for the product;

Fuestions such as these must $e answered $& an engineering designgroup familiar with methods of preconstruction cost estimating $ased onprocess and preliminar& plant design principles"

Process Design

The *uestion of what is the $est process for producing the product$ears on the important su$ect of process design" The process informa!tion re*uired for process design comprises the following# (l) ivrittendescription of the process% (=) notes regarding special safet& precautions,possi$le operating peculiarities, chemical reactions, and properties ofmaterials of construction% (>) knowledge of all raw materials, products,and %Intermediate process!*uantities in convenient and appropriate units%(@) knoivledge of all process temperatures, pressures, and concentrations%() knowledge of ph&sical characteristics and chemical compositions andproperties of all raw materials, products, and intermediate processmaterials under operating conditions% (B) heat, material, and energ&

$alances around all signi0cant operations or pieces of e*uipment" Thecomplete $alances around process e*uipment as such (a still, a fractionat.ing tower, etc") should $e attempted% $ut some of the $alances, such asenerg& $alances around nonstandard e*uipment, can $e onl& generaland appro+imate, pending engineering design, procurement of e*uip!ment, and information on manufacturers speci0ed operating e0iciencies%etc"% () a complete diagrammatic process 4ow sheet which shows the4ow of the process streams and ta$ulates conditions at the appropriatepoints on the process streamlines and e*uipment sketches where con!venient" A t&pical process 4ow sheet is shown in Gig" >!@"

Preconstzucticn Cost Estimation

After the process information has $een integrated into one or more 4owsheets, the economic aspects of 7the design are ne+t considered" Thisinvolves ( 1) an estimate of the t&pes and sies of e*uipment and materials,$uildings, ground area, and utilit& facilities% (=) a determination of whatthe process +vill cost $ased on ph&sical facilities and construction charges%(>) a cost estimate of utilities consumption (steam, electricit&, ivater, fuel),la$or and supervision personnel re*uirements, maintenance and repairs,raw materials!and 0nance charges!(interest, ta+es, insurance, medical$ene0ts, eta)"

9n this economic $asis, a suita$le process design can $e chosen andrecommendations presented in a preliminar& report to compan& e+ecu!tives for a decision on the proect"

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Design and Selection cf Chemical Engineering Equipment

In the design of all chemical processing e*uipment, it is important to

remem$er that success depends on continuous performance and thedesigner should recognie unit operations and unit processes as the $asisfor selection and design" The designer is concerned primaril& in specif&!ing an economical s&stem or piece of e*uipment suita$le for a speci0cchemical operation" aturall&, this involves pro$lems of temperature,pressure, corrosion, erosion, metal fatigue, and other considerations suchas relief from overpressure or vacuum"

2esign $ased upon standard e*uipment is of primar& importance"Re*uirements for the $asic designs of chemical processing e*uipment arepresented in esta$lished codes% these are fre*uentl& alter!ed in accordancewith e+periences ac*uired" :riting of speci0cations on special e*uip!ment for successful operation is e*uall& the task of 3the designer, should

standard e*uipment not $e availa$le to carr& on the speci0c operation"A good design will provide for the processing, handling, and storage ofchemical materials in $atch andor continuous s&stems, +vhich are pro!ductive and safe under the conditions involved"

Bases for Good Design

Jood designs do not happen% the& are founded on rvell!knoivn, soundprinciples" To create a good chemical engineering design, it is necessar&to possess an interest in and a genuine lil!aing for chemical plant la&outand for solving engineering pro$lems, together with a facult& of koen,appreciative 9$servation, and the a$ilit& to anal&e conditions and data"

The chemical engineer accumulates data and determines in minute detailthe varia$les that must $e kept under control to ensure econom& andsuccess" Grom these data" he makes preliminar& designs for the plantand writes speci0cations for the e*uipment and the materials needed"He indicates t&pes and sies of commercial e*uipment, the feasi$ilit&and conditions of economic operation, and supplies information for $uild!ing and often for designing special e*uipment" The technical skillsre*uired in design involve a comprehensive training in mechanics, engi!neering drawing, electricit&, thermod&namics, materials of construction,materials handling, 4uid d&namics, chemistr&, ph&sics, and mathematics"

In the 0nal anal&sis, the development through details should $e dele!3gated to technicians and draftsmen% $ut a good engineer must himself $esu4icienti& skilled so that he can conve& his thoughts clearl& for othersreadil& to interpret" 9ne of the most important means of communica!tion of design ideas is through the use of engineering graphics skills"

Drawings and odels in Process and Plant Design

The representation of design ideas and the assem$l& of informationfor purposes of manufacture, construction, and erection of structures ande*uipment are done largel& through ciranrings and models" Gor the aver!age chemical process plant, it is estimated that the cost of preparing these

items of design ranges from > to B per cent of the total created plant cost"-ketches, schematic diagrams, engineering drawings of var&ing degreeof detail, and three!dimensional models are used in process and plant

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of Gigs" 1!1 and 1!=, the assem$l& of the detailed parts re*uires a shopassem$l& drawing 7vith necessar& code and speci0cations of parts to allowthe 0nal assem$l& and erection" Gor complicated machiner& such as thegrit washeri several unit ar su$assem$l& drauings of groups of parts arere*uired to ena$le the shop mechanic to assem$le the complete machineeasil&" The design and manufacture of comple+ e*uipment ma& re*uirea total of several hundred drawings under classi0cations 1 through @"

" 9utline "Assem$l& or Jeneral Arrangement 2rauings" The chemicaldesign engineer must pian for the proper la&out of e*uipment and thusneeds a general idea of the e+terior shape and principal dimensions of eachpiece of e*uipment used in the process" Gor this purpose, general

arrangement drawings of the t&pe "shown in Gig" 1.> are availa$le fromthe vendor or from the e*uipment design group 7within the compan&"2etailed design information such as disassemhl& and over!all clearancere*uirements, anchor $olt locations, and piping connections are fre!*uentl& included"

B" E*uipment Installation 2ramaga" Dendor prints which show thedetails and installation se*uencing of purchased e*uipment are routinel&supplied to the design and construction groups" Accuratel& dimensionedmounting details for heav& machiner&, 4ow diagrams, and electric powerand instrumentation drawings are e+amples of the drawings re*uiredfor proper installation and operating performance"

Plant Design DrawingChemical plants cannot $e put together inrandom fashion" Careful planning and integration of all process e*uip!ment and au+iliaries such as piping, electric power, and instrumentationare done through drawings and models"

1" Plant Layout Drawing After principal e*uipment has $een speci!0ed, seale models are usuall& constructed and arranged $& plant la&outdesign for optimum feasi$ilit& of operation (Gigs" !@ and !)" Assem$l&dra+vings in plan and elevation can $e prepared for a permanent recordof general la&out arrangements of the entire plant from which construc!tion and installation drawings can $e detailed $& draftsmen"

=" Construction and Installation Dramaga" Ail parts of the plant aredrawn in consider!a$le detail to scale to show position of e*uipment andconnections, foundations, supports, overhead structures, etc", so that

ever& re*uired item of plant e*uipment can $e 0tted into the desiredarrangement $& a construction cre+v" 2rawings classi0ed under thiscategor& are#

a" Plot plane

$" Goundation plans, including erection details

c" -tructure plans, including erection details

d" Piping drawings (Gigs" O!= to O!B)

c" Electrical drawings, iargel& schematic (see Gigs" !=K and O!=> fors&m$ols)

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f" Instrumentation drawings, largel& schematic (see Gig" >!1K fors&m$ols)

Drafting Procedures2rafting of design re*uirements $& means of drawings is a time!con!suming operation and there$& e+pensive" The use of three!dimensionalmodels of chemical plants has ver& eQectivel& reduced drawing re*uire.ments, $ut man& two!dimensional drawings are still re*uired" A fewwords a$out ef8cient methods of planning and e+pediting drawings andreproductions would $e in order $& wa& of review"Drawing Instruments"2rafting machine"; :hich com$ine the func!tions of T s*uare, triangles, protractor, and scales are used e+clusivel& incommercial drafting rooms" / atur!driver% rotating erascrs are nowemplo&ed in com$ination 7with shields for correcting errors and makingchanges" Hand lettering is reduced to a minimum $& use of i&pingmuch!inca, particularl& for drawings 'where design notes and speci0cationsare included with the drawing on one sheet" /an& t&pes of templates

are availa$le for drawing commonl& used s&mhols"

Drafting Scales" The choice of correct scales and precision of measure!merit is a matter of e+perience" The $est soale is one that presents aclear, graphic description within the precision of measurement re*uired"Highl& cengested drawings should $e avoided $ecause of the additionaltime re*uired to produce and to interpret the drawings"

It should $e o$vious that dimensioning re*uirements for machine!shopwork is much more e+act than the re*uirements for process plant con.struction drawings" In the latter case, center!line locations of principalprocess e*uipment must $e speci0ed $& scale drawings to give a precision

of i 1 in" This can $e achieved $& a generall& used soale of O in" 1 ft"The soale is increased to >@ in" 1 ft where more detail is re*uired orwhere the drawing $ecomes unusuall& congested" Gor an over!all la&outthe scale is reduced to >!@ or k% in" 1 ft" 9nce the e*uipment is located$& this t&pe of center!line scaling procedure, the working dimensionsre*uired for installation and repair procedures are shown directl& on thedrawings"

Reproduction /ethods" Pencil drawings on a good!*ualit& tracingpaper can $e directl& reproduced as $lueprints or $& the newer processesgiving $lacie, red!, &ellow!, or $lue!on!white prints" The latter method

is $eing adopted throughout the industr& since these prints are easier toread, as well as to reproduce and reduce $& photo!graphic procedures"The reproduction machines are smaller and porta$le and emplo& a fast!dr&!process procedure" 5lueprints are still produced $& drafting 0rmswhich have made a high investment in $lueprint machines and cannoteconomicall& aQord a change!over,

"se of #igh$speed Computers

There are man& tools used through the entire development of a com!mercial process $ut none 7vill contri$ute as much as high!speed computingmachiner& when properl& utilied" Gor this reason a special section in

this 9rientation chapter will stress the applications of this relativel&new tool in the chemical industr&"

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High!speed computers consist of electronic circuits and mechanicalparts coupled together in such a manner that nearl& ever& conceiva$leoperation in mathematics can $e performed at ver& high speeds" 3An&process which can $e reduced to mathematical Ianguage, i"e", addition,su$traction, multiplication, division, integration, and diQerentiation, isadapta$le to and should $e considered for high!speed computing" /an&pro$lems encountered in process development and design can $e solvedrapidl& with a higher degree of completeness with high!speed computersat less mone& than 7vas heretofore possi$le +vith slide rules and deskcalculators" 9verdesign and safet& factors can $e reduced 7vith a su$!stantial savings in capital investment"!!%&pical 'pplications!-ome of the applications of high!speed comNputers in the development of a chemical process are listed ne+t withspeci0c reference to chapters in this $ook +vhere such pro$lems areencountered#

1" -tatistical correlation of datar!la$orator& and pilot plant data fordesign purposes% plant data for *ualit& control and trou$le shooting(Chap" >)"

=" Preparation of process 4ow sheets!material and energ& $alances,particularl& on rec&cle operations% ultimatel& can incorporate man&process varia$les into a general design optimiation (Chups" >, @, and B)"

>" -election of e*uipment!man& e*uipment design pro$lems re*uiretrial and error or comple+ mathematical solution% e+amples are a$sorp!tion, distillation, humidi8cation!dehumidi0catiom evaporation, e+trac!tion, 0uid 4ow, and heat e+change (Chap" @)" S @

@" Economic evaluatiom!solution of cost e*uations for optimiationof process and e*uipment selection% this is also a part of items = and >(Chaps" >, @, and 5)"

" Piping design studies!stud& of piping forces to o$tain points ofma+imum stress% proper location of pipe supports (Chap" O)"

B" Instrumentation and control!stud& of controi loops for properprocess control design and operation (Chap" O)"

" Plant operations!operations research and linear programming ofthe commercial plant for ma+imum economic returns% cost accounting,pa&roll preparation, and other $usiness procedures"

%&pes of Computers" High!speed computing machiner& can $e dividedconvenientl& into two t&pes $ased on their mode of operation" Thedigital cmnputer is a ver& fast calculator performing $asicall& additionand su$traction with multiplication and division possi$le $& a repetitiveseries of $asic operations" -uch machines are e+pensive to install andprogram via punch cards, are more precise, capa$le of repetitive operationon the same t&pe of pro$lem, and produce solutions in ta$ular form on

t&ped sheets" The cost of the digital computer depends on the speedof operation and the num$er of its memor& units or spaces where numer.ical information can $e 0led for future se*uential mathematical process!

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ing" -mall units capa$le of solving simple pro$lems cost around K,KKK,while large machines will re*uire an e+penditure of KK,KKU) or more"In some cases it is possi$le to rent the larger machines"

Analog computers are essentiall& electronic amplif&ing circuits capa$leof solving diiierential e*uations without the use of numerical methodsre*uired for digital +vork" The eQect ofra comple+ set of varia$les on aprocess can $e studied ivithout an e+pensive card programming" Theresultant electronic output data as the answer can $e automaticall& plotted for a

permanent record" The inherentaccurac& of this t&pe of machine is not as good asthat of the digital" It ranges from K"1 to = per cent, depending on the electroniccomponents, $ut the analog

computer is usuall& less e+pensive to purchase and operate than a digitalcomputer" Gor e+ample, a kit can $e purchased and assem$led forstudent training for less than =>KV Analog computers also have thedisadvantage of lack of memor& storage re*uired for optimiation studies"Engineers should $ecome familiar with the capa$ilities of thesemachines and use them to the utmost" It is onl& then that the large

investment in this tool for the chemical industr& urilI pa& oQ" /ostcolleges now have $oth digital and analog e*uipment so that the instructorin plant design should have the class solve a few simple pro$lems $& thismeans" Gurther stud& references in this area are listed in the Additional-elected References at the $ack of the $ook"