CHE 481 TEST 1

Chapter 1 EOC Problems 1. What are are the three three principle principle types of diagrams used used by process process engineers to describe the ow of chemicals in a process? On which of these diagrams would you expect to see the following items? a. emperature and pressure pressure of a process process stream! stream! P"# b. O$er$iew O$er$iew of of a multip multiple%un le%unit it proces process! s! &"# &"# c. 'a(or 'a(or Contr Control ol )oop! )oop! P"# d. Press Pressur ure e *ndicat *ndicator or!! P+*# e. Press Pressur ure%r e%reli elief ef $al$e! $al$e! P+*# P+*# ,. - problem problem has occurred occurred in the measuring measuring element element of a le$el%indicating le$el%indicating controller in a batch reactor. o what principle diagram should you refer in order to troubleshoot the problem? P+*# . Why is it important for for a process process engineer engineer to be be able to re$iew a three% dimensional model /actual or $irtual0electronic of the plant prior to the construction phase of a pro(ect? o chec2 for clearance3 accessibility3 layout of e4uipment3 piping3 and instrumentation instrumentation 5. 6ame 7$e things things that that would would a8ect the the locations locations of di8eren di8erentt pieces pieces of e4uipment when determining the layout of e4uipment in a process unit. a. Clearance Clearance for for tube bundle bundle remo$a remo$all on a heat exch exchanger anger b. 6P9: on a pump%a8ec pump%a8ects ts the $ertical $ertical separ separation ation of feed feed $essel $essel and pump inlet c. -ccessi -ccessibili bility ty of an instr instrument ument for an operator operator d. 9eparatio 9eparation n between between e4uipmen e4uipmentt for safety safety reason reasons s e. Crane Crane access access for remo$ing remo$ing e4uipmen e4uipmentt f. ;ertical ertical position position of of e4uipment e4uipment to allow allow for for gra$ity gra$ity ow of of li4uid li4uid g. :ydrostatic head for thermosiphon thermosiphon reboiler reboiler%a8ects %a8ects height height of column s2irt <. Why are are accurate plant models /made of plastic plastic parts parts no longer longer made as part of the design process? What function did these models play and how is this function now achie$ed? 6o longer made because they are too expensi$e and di=cult to change0re$ise. change0re$ise. he models ha$e been replaced with $irtual0E% model using C-#. hey allow re$ision of critical e4uipment and instrument placement to ensure access3 operability3 and safety >. *n the context context of process process modeling tools3 what does O9 and *9 stand stand for? O9%Operator raining 9imulation *9%*mmersi$e raining 9imulation @. What is is augment augment realit reality? y? Ai$e Ai$e one exampl example e of it. it. B. here are are two common common reasons reasons for ele$ating ele$ating the bottom of a tower by means of s2irt.D One is to pro$ide enough 6P9: for the bottoms product pump to a$oid ca$itation. What is the other reason? Pro$ide enough hydrostatic head dri$ing force to operate a thermosiphon reboiler . What is the purpose purpose of a pipe rac2 in a chemical chemical process? process? Pro$ides Pro$ides a clear clear path for piping within and between processes. *t 2eeps piping o8 the ground to eliminate tripping haFards and ele$ates it abo$e roads to allow $ehicle access 1G.When would a structure%mounted structure%mounted $ertical plant layout arrangement be preferred o$er a grade%mounted3 horiFontal3 in%line arrangement? When land is at a premium and the process must ha$e a small foot print. he

disad$antage is that it is more costly because of the additional structural steel 11.Which of the principle diagrams should be used to do the following? a. 6umber of trays in distillation column? P"# b. #etermine top and bottom temperatures in a distillation column? P"# c. ;alidate the o$erall material balance for a process? P"# d. Chec2 the instrumentation for a gi$en piece of e4uipment in a pre% start%upD re$iew? P+*# e. #etermine the o$erall material balance for a whole chemical plant? -ll &"# or P"# 1,.- process that is being considered for construction has been through se$eral technical re$iews bloc2 ow3 process ow3 and piping and instrumentation diagrams are a$ailable for the process. Explain the changes that would ha$e to be made to the following three principal diagrams if during a 7nal preconstruction re$iew3 the following changes were made! a. he e=ciency of a 7red heater has been speci7ed incorrectly as ,H instead of B,H. P"# b. *t has been decided to add a second /bac2up dri$e for an existing compressor. P+*# c. he locations of se$eral control $al$es ha$e been changed to allow for better operator access. Plant )ayout and Ele$ation d. Pipes located at ground le$el present a tripping haFard. Pipe isometrics 1.Explain how each of the following statements might a8ect the layout of process e4uipment a. - speci7c pump re4uires a large 6P9:. E4uipment should be ele$ated abo$e pump to allow enough 6P9: for pump b. he ow of li4uid from an o$erhead condenser to the reux drum is gra$ity dri$en. "low by gra$ity so condenser should be ele$ated abo$e reux drum c. Pumps and control $al$es should be located for easy access and maintenance. 9hould be located for easy access on ground or on accessible platforms d. 9hell%and%tube exchanges may re4uire periodic cleaning and tube bundle replacement. 9hould ha$e enough space for cleaning and replacement of bundle and crane mo$ement e. 15.

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Chapter , EOC Problems 1. What are the 7$e elements of the hierarchy of process design? a. &atch or Continuous Process b. *nput%Output structure of Process c. Iecycle structure of process d. Aeneral separation structure of process e. :eat%exchanger networ20process energy reco$er ,. What are the three types of recycle structures possible in a chemical process? Explain when each is used. a. 9eparate0purify unreacted feed and recycle%use when separation is feasible b. Iecycle without separation but with purge%when separation of unused reactants is infeasible0uneconomic. Purge is needed to stop build up of product or inerts. c. Iecycle without separation or purge%product0byproduct must react further through e4uilibrium reaction . Ai$e three criteria for choosing a batch process as opposed to a continuous process. a. 9mall 4uantities re4uired b. &atch%to%batch accountabilities re4uired c. 9easonal demand for product or feed stoc2 a$ailability d. 6eed to product multiple products using the same e4uipment e. 9low reactions f. :igh e4uipment fouling g. 5. When would one purposely add an inert material to a feed stream? *llustrate this strategy with an example3 and explain the ad$antages /and disad$antages of doing this. 9team added to catalytic reaction using hydrocarbon feeds to pro$ide energy for the desired endothermic reaction and to force the e4uilibrium towards styrene product. <. *n general3 when would one purify a material prior to feeding it to a process unit? Ai$e at least one example for each case you state. a. *f the impurity foul or poison a catalyst used in the process. Iemo$e trace sulfur compounds in natural gas prior to sending them to the steam reforming reactor to produce hydrogen b. *f impurities react to form di=cult%to%separate or haFardous products0byproducts. /Production of isocyanates using phosgene. CO is formed $ia steam reforming of C:5 to gi$e CO and :,. :, must be remo$ed from CO prior to reaction with C), to form :C) c. *mpurity is present in large 4uantities it may be better to remo$e the impurity than ha$ing to siFe all the down stream e4uipment to handle the large ow of the inert material. /9uing oxygen rather than air to 7re a combustion. Iemo$ing nitrogen reduces e4uipment siFe >. Pharmaceutical products are manufactured using batch process because! a. they are usually re4uired in small 4uantities b. batch%to%batch accountability and trac2ing are re4uired by the "ood + #rug

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Chapter > EOC Problems 9tate two common criteria for setting the pressure of a distillation column. a. 9et based on the pressure re4uired to condense the o$erhead steam using cooling water b. 9et based on highest temperature of bottom product that a$oids decomposition or reaction c. 9et based on a$ailable highest hot utility for reboiler 9uggest two reasons each why distillation columns are run abo$e or below the ambient pressure. Iun a distillation column abo$e ambient pressure because! a. he components to be distilled ha$e $ery high $apor pressures /$ery lightD components and the temperatures at which they can be condensed at or below ambient pressure are K cooling water. hus3 we run the column at high pressure to a$oid the use of refrigeration in the condenser b. he siFe of the column /diameter reduces at the pressure decreases. -lthough the separation is usually more di=cult at higher pressures3 it may be more cost e8ecti$e to run the column at or abo$e atmospheric pressure Iun a distillation column below ambient pressure a. he components re4uiring separation ha$e $ery low $apor pressures /$ery hea$yD components and if distilled at ambient pressure would re4uire excessi$ely high temperatures to reboil b. "or thermally sensiti$e materials3 e.g. foods3 pharmaceuticals3 and some organics3 the bottom temperature in an atmospheric column might cause the material to decompose or react. "or such systems3 the pressure is reduced below atmospheric to a point where the bottom temperature does not cause thermal degradation of the product. 9uggest two reasons why reactors are run at ele$ated pressures and0or temperatures. Iun reactions at ele$ated temperature because a. he rate of reaction rate is faster. his results in a smaller reactor and0or higher single%pass con$ersion b. he reaction is endothermic and e4uilibrium limited and increasing the temperature shifts the e4uilibrium to the right Iun reaction at ele$ated pressure because c. he reaction is gas phase and the concentration and hence rate is increased as the pressure is increased. his results in a smaller reactor and0or higher con$ersion d. he reaction is e4uilibrium limited and there are fewer product moles than reactant moles. -n increase in pressure shifts the e4uilibrium to the right. Ai$e two reasons why operation of a process at greater than ,
c. Examples for doing this for a reactor are to! increase the reaction rate or impro$e e4uilibrium for an endothermic reactor. -n example for doing this for a distillation column is! to pro$ide a $apor%li4uid system for a hea$y /high boiling point component <. #e7ne a condition of special concern.D #e7ne two such conditions3 and state one possible (usti7cation for each. - conditionD of special concern is a process condition that de$iates from an idealD or low%costD operating conditions. Operating at pressures outside the range of 1%1G atm or temperatures outside of the range 5<%,. *n the food and drug industries3 many processes used to produce new acti$e ingredients /drugs or to separate and purify drugs and foods occur at $acuum conditions and often at low temperatures /less than room temperature. What is it about these types of products that re4uires that these conditions of special concern be used? 'any of these products are thermally liable meaning that they degrade at 4uite low temperatures. he use of $acuum conditions allows $apor%li4uid e4uilibrium and $aporGsolid e4uilibrium /freeFe drying or lyophiliFation to occur at temperatures below which thermal degradation occurs. @. "or the separation of a binary mixture in a distillation column3 what will be the e8ect of an increase in column pressure on the following $ariables? a. endency to ood at a 7xed reux ratio. Will decrease because the density of $apor will increase and hence the super7cial $elocity in the tower will decrease thus mo$ing away from ooding b. Ieux ratio for a gi$en top and bottom purity at a constant number of  stages. Will increase with pressure. his is because as pressure increases3 the separation becomes more di=cult and the e4uilibrium line mo$es closer to the xy line. he only way to compensate is therefore to increase the reux ration that in turn increases the internal ows in the column%hence the $apor ow and $elocity will increase and mo$e the column towards ooding. c. 6umber of stages re4uired for a gi$en top and bottom purity at constant reux ratio. he number of stages will increase with pressure for the same reason gi$en in /b abo$e. d. O$erhead condenser temperature. -s pressure increases3 the condenser temperature will increase% this is consistent with -ntoineMs e4uation that as temperature increases so does the $apor pressure.