CHAPTER 11 -HEURISTICS.pptx

8/20/2019 CHAPTER 11 -HEURISTICS.pptx

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CHAPTER 11

Utilizing Experience-BasedPrinciples to Confrm the S ita!ilit"

o# a Process $esign


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Chemical engineers have the skills to perform detailed andaccurate calculations for design, analysis, and operation ofequipment and chemical processes.Experienced chemical engineers have formulated a number of

experience-based shortcut calculation methods (ie heuristics)and guidelines for!. Checking ne" process designs#. $roviding equipment si%e and performance estimates

&. 'elping troubleshoot problems "ith operating systems. erifying that results of computer calculations * simulations

are reasonable.+. $roviding reasonable initial values for input into a process

simulator required to achieve program convergence. btaining approximate costs for process units


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0he characteristics of any heuristic

!. 1 heuristic does not guarantee a solution#. 2t may contradict other heuristics&. 2t can reduce the time to solve a problem

. 2ts acceptance depends on the immediate context

instead of on an absolute standard.


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2n 3Chapter 4nderstanding $rocess Conditions5, process units and streamconditions that "ere identi6ed as areas of special concern "ere analysed.

0hese areas "ere highlighted in a series of informational tables, eg


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2n this chapter, the analysis of chemical processes "ill be completed bychecking the equipment parameters * stream conditions in the $7/ foragreement "ith observation and experiences in similar applications.

0he required information to start an analysis is providedin a series of in#ormation ta!les containing shortcutcalculation techniques.

0he use of these resources "ill be demonstrated bychecking the conditions given in the basichydrodealkylation $7/.


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11%1 THE R&'E &( E)PER*E+CE *+ THE $ES*,+PR&CESS11%1%1 *ntrod ction to Technical He ristics andShortc t ethods

1 he ristic is a statement concerning equipment si%es,operating conditions, and equipment performance thatreduces the need for calculations.

1 shortc t method replaces the need for extensivecalculations in order to evaluate equipment si%es,operating conditions, and equipment performance.

8uidelines and heuristics must be applied "ith an

understanding of their limitations.


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11%1%. aximising the !enefts o!tained #romexperience

0o bene6t fully from experience, it is important to make aconscious e9ort to use each ne" experience to build afoundation upon "hich to increase your ability to handleand solve ne" problems.

0he process by "hich an engineer uses information andcreates ne" heuristics consists of & steps 0he $1:process!. $redict

#. 1uthenticate ; 1nalyse


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!. Predict 0his is a precondition of the $1: process. 2trepresents your best prediction of the solution. 2t ofteninvolves making assumptions and applying heuristicsbased on experience.

#. A thenticate / Anal"se 2n this step, you seek outequations and relationships, do research relative to theproblem, and perform the calculations that lead to"ards asolution.


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Example !!.!Evaluate the 6lm heat transfer coe>cient for "ater at C?o"ing at&.A+ m;s inside a &Bmm diameter tube. 7rom previousexperience, you kno" that the 6lm heat transfercoe>cient for "ater, at C and !.B& m;s, in these tubes is+#+A cient +#+A


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it is found that the :eynolds number for the "ater in thetubes is:e u D; (!.B&)(FF . )(!.+)(A.A#+ );(F.B x ) ! x

(ie turbulent ?o"). 4se the =ieder-0ate equation to check the prediction

h/;k (A.A#&) (!!.!

0ake ratio of equation (!!.!) for the t"o conditions given above,and rearrange and substitute numerical values. 4sing G to identifythe ne" conditions at C,

hH;h (!!.#) (!)(!.+A)(A.F &)(!. &)(!.AA)(!.AB) #. #+

(!!.&) hH (#. #+)(+#+A)


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hH (#. #+)(+#+A)


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11%. PRESE+TAT*&+ &( TAB'ES &( TECH+*CA'HEUR*ST*CS A+$ ,U*$E'*+ES


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Example !!.#

:efer to the info given in Chapter ! for the toluenehydrodealkylation process, namely, 7ig !. and 0ables !.+and !. . 4sing the info provided in the tables in thischapter !!, estimate the si%e of the equipment and otheroperating parameters for the follo"ing units(a) -!A#(b) E-!A+

(c) $-!A!(d) C-!A!(e) 0-!A!(f) '-!A!

Compare your 6ndings "ith the info given in Chapter !.


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.


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Estimate the si%e of the equipment and other operating


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q p p gparameters for the follo"ing units -!A#

Compare your 6ndings "ith the info given in Chapter !.(a) -!A# 'igh $ressure $hase =eparator

7rom 0able !!. , the follo"ing heuristics are used:ule & ertical vessel:ule J;/ bet"een #.+ and + "ith optimum at &.A:ule + Jiquid hold-up time is + minutes based on K volume ofvessel:ule F 8as velocity is given by

u k m;s "here k A.A&A+ for vessels "ithout mesh entrainers:ule !# 8ood performance obtained at &AL - !AAL of u from :ule

F.

•


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7rom 0able !.+apour ?o" =tream B F#AAkg;h, $ #&.F bar, 0 C

Jiquid ?o" =treams ! M !B !!,+ A kg;h, $ #.Bbar, 0 C B kg ; and B+A kg ;(estimated from 0able !. )

7rom :ule F, u A.A&A+ A.&!& m;s

4se (A. +)(A.&!&) A.#& m;sNo" mass flo" rate of vapour uO; F#AA;& AA #.+ kg;s=olving for / !.&&m.

•

7 l + th l f li id A + J O A # J


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7rom :ule +, the volume of liquid A.+ J O; A. # J+ min of liquid ?o" (+)( A)(!!,+ A);B+A;& AA !.!&Equating the t"o results above, J !.+ m

7rom :ule , J;/ should be in the range #.+ to +. 7or this caseJ;/ !.+ ;!.&& !.! . Pecause it is out of range, change to

J #.+/ &.&m. 'euristics from 0able !!. suggest that -!A# should be a vertical vessel "ith / !.&&m, J &.&m.

7rom 0able !. , the actual -!A# is a vertical vessel "ith / !.!m, J &.+m.

0hus it can be concluded that the design of -!A# in Chapter

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CHAPTER 11 -HEURISTICS.pptx