Types Of Reactors
Types of Reactors There are following different types of reactors: 1. 2. 3. 4. ".
Contin Continuou uouss stirred stirred tank tank react reactor or.. Fixe Fixed d bed bed rea react ctor or.. Tabul abular ar reac reacto torr. o!i o!ing ng bed bed react reactor or.. Flui Fluidi di#ed #ed bed bed reac reacto torr.
There description is as follows:
1. Continuo Continuous us stirre stirred d tank tank reactor reactor The continuous flow stirred$tank reactor %C&T'() also known as !at$ or back*ix reactor) is a co**on ideal reactor type type in che*ical in che*ical engineering. engineering. + C&T' often refers to a *odel used to esti*ate the key unit operation !ariables when using a continuous agitated$tank reactor to reach a specified output. The beha!ior of a C&T' is often approxi*ated or *odeled by that of a Continuous ,dea ,deall lly y &tir &tirre red$ d$T Tank ank 'eac 'eacto torr %C,& %C,&T' T'(. (. +ll +ll calc calcul ulat atio ions ns perf perfor or*e *ed d with with C,&T C,&T's 's assu*e perfect assu*e perfect *ixing. ,n *ixing. ,n a perfectly *ixed reactor) the output co*position is identical to co*position of the *aterial inside the reactor) which is a function of residence ti*e and rate of reaction. ,f the residence ti*e is "$1- ti*es the *ixing ti*e) this approxi*ation is !alid for engineering purposes. The C,&T' *odel is often used to si*plify engineering calculations and can be used to describe research reactors. ,n practice it can only be approached) in particular in industrial si#e reactors.
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Types Of Reactors
,n a continuous$flow stirred$tank reactor %C&T'() %C&T'( ) reactants and products are continuously added and withdrawn. ,n practice) *echanical or hydraulic agitation is reuired to achie!e unif unifor or* * co*p co*pos osit itio ion n and and te*p te*per erat atur ure) e) a choi choice ce stro strong ngly ly infl influe uenc nced ed by proc proces esss considerations. The C&T' is the ideali#ed opposite of the well$stirred batch and tubular plug$ flow reactors. +nalysis of selected co*binations of these reactor types can be useful in uantitati!ely e!aluating *ore co*plex gas$) liuid$) and solid$flow beha!iors.
(Continuous stirred tank reactors, (a) With agitator and internal heat transfer surface, (b) With pump around mixing and external heat transfer surface).
/ecause the co*positions of *ixtures lea!ing a C&T' are those within the reactor) the the react reactio ion n dri! dri!in ing g forc forces) es) usua usuall lly y the the react reactan antt conce concent ntrat ratio ions ns)) are are nece necessa ssaril rily y low low. Therefore) except for reaction orders #ero$ orders #ero$ and negati!e) a C&T' reuires the largest !olu*e of the reactor types to obtain desired con!ersions. 0owe!er) the low dri!ing force *akes possible better control of rapid exother*ic and endother*ic reactions. hen high con!ersions of reactants are needed) se!eral C&T's in series can be used. ually good results can be obtained by di!iding a single !essel into co*part*ents while *ini*i#ing back$*ixing and short$circuiting. The larger the nu*ber of C&T' stages) the closer the perfor*ance approaches that of a tubular plug$flow reactor. Continuous$flow stirred$tank reactors in series are si*pler and easier to design for isother*al operation than are tubular reactors. 'eactions with narrow operating te*perature ranges or those reuiring close control of reactant concentrations for opti*u* selecti!ity benefit fro* series arrange*ents. ,f se!ere heat$transfer reuire*ents are i*posed) heating or cooling #ones can be incorporated within or external to the C&T'. For exa*ple) i*pellers or centrally *ounted draft tubes circulate liuid upward) then downward through !ertical heat$exchanger tubes. ,n a si*ilar fashion) reactor contents can be recycled through external heat exchangers.
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Types Of Reactors
pplications! i.
ii.
iii.
iv. iv.
!.
,n industry) a packed colu*n is a type of packed bed used to perfor* separation processes)) such as absorption processes absorption)) stripping stripping)) and distillation distillation.. + packed colu*n is a pressure a pressure !essel that has a packed section. Colu*ns used in certain types of chro*atography of chro*atography consist consisting ing of a tube filled with packing *aterial can also be called packed colu*ns and their structure has si*ilarities to packed beds. The colu*n colu*n can be filled filled with with rando* rando* du*ped du*ped packin packing g %creati %creating ng a rando* rando* packed packed colu*n( colu*n( or with structured packing sections) sections) which are arranged or stacked %creating %creating a stacked packed colu*n(. ,n the colu*n) liuids tend to wet the surface of the packing and the !apors pass across this wetted surface) where *ass transfe transfer r takes takes place. acking *aterial can be used instead of trays to i*pro!e separation in distillation colu*ns. acking offers the ad!antage of a lower pressure drop across the colu*n %when co*pared to plates to plates or trays() trays() which is beneficial while operating under !acuu*. iff iffer eren ently tly shap shaped ed packin packing g *ateri *aterials als ha!e ha!e differ differen entt surface surface areas areas and !oid !oid space space between the packing. /oth of these factors affect packing perfor*ance.
". #acked #acked bed re react actors ors acked bed reactors can be used in che*ical che*ical reaction. These reactors are tubular tubular and are filled with solid catalyst particles) *ost often used to cataly#e gas reactions. The che*ical reaction takes place on the surface of the catalyst. catalyst. The ad!antage of using a packed bed reactor is the higher con!ersion per weight of catalyst than other catalytic reactors. The con!ersion is based on the a*ount of the solid catalyst rather than the !olu*e of the reactor.
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Types Of Reactors
$. Tubular reactor or plug plug flo% reactor reactor + tubular reactor is a !essel through which flow is continuous) usually at steady state) and config configure ured d so that that con!er con!ersio sion n of the che*ica che*icals ls and other depend dependent ent !ariabl !ariables es are functions of position within the reactor rather than of ti*e. ,n the ideal tubular reactor) the fluids flow as if they were solid plugs or pistons) and reaction ti*e is the sa*e for all flowing *ater *aterial ial at any any gi!e gi!en n tube tube cros crosss secti section on.. Tubul ubular ar react reactor orss rese* rese*bl blee batc batch h react reactor orss in pro!iding initially high dri!ing forces) which di*inish as the reactions progress down the tubes. Flow in tubular reactors can be la*inar be la*inar ) as with !iscous fluids in s*all$dia*eter tubes) tubes) and greatl greatly y de!iate de!iate fro* fro* ideal ideal plug$f plug$flow low beha!io beha!ior) r) or turbulent) as with with gases gases.. Turbulent flow generally is preferred to la*inar flow) because *ixing and heat transfer are i*pro!ed. For slow reactions and especially in s*all laboratory and pilot$plant reactors) establi establishi shing ng turbul turbulent ent flow flow can result result in incon! incon!enie enientl ntly y long long reacto reactors rs or *ay reuir reuiree unacceptably high feed rates.
Tubular reactors are always used in a continuous flow *ode with reagents flowing in and products being re*o!ed. They can be the si*plest of all reactor designs. Tubular reactors are often referred to by a !ariety of na*es:
ipe reactors acked$bed reactors Trickle$bed reactors /ubble$colu*n reactors bulating$bed reactors
&ingle$phase flow in a tubular reactor can be upward or downward. Two$phase flow can be co$current up$flow) up$flow) counter$current %liuid down) gas up( or) *ost co**only) co**only) co$current down$flow.
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Types Of Reactors Tubular reactors can ha!e a single wall and be heated with an external furnace or they can be 5acketed for heating or cooling with a circulating heat transfer fluid. xternal furnaces can be rigid) split$tube heaters or be flexible *antle heaters.
pplications! Tubular reactors are used in a !ariety of industries:
etroleu*) etroleu*) etroche*ica etroche*ical) l) oly*er oly*er.. har*aceutica har*aceutical) l) aste Treat*ent Treat*ent)) &pecialty &pecialty Che*ical) +lternati!e nergy
Tubular reactors are used in a !ariety of applications:
Carbonylation) ehydrogenation) 0ydrogenation) 0ydrocracking) 0ydrofor*ulation) 6xidati!e deco*position) artial oxidation) oly*eri#ation) 'efor*ing
,t is often desirable to si#e a tubular reactor to be large enough to fit 7 to 1- catalyst particles across the dia*eter and be at least 4-$"- particle dia*eters long. The length to dia*eter ratio can be !aried to study the effect of catalyst loading by euipping the reactor with 8spools9 to change this ratio.
&. 'oing 'oing bed re react actor or ,n *anufacturing) the si*ulated *o!ing bed %&/( process is a highly engineered process for i*ple*enting chro*atographic separation. ,t is used to separate one che*ical co*p co*pou ound nd or one one clas classs of che* che*ic ical al co*p co*pou ound ndss fro* fro* one one or *ore *ore othe otherr che*ical co*pounds to co*pounds to pro!ide significant uantities of the purified or enriched *aterial at a lower cost than could be obtained using si*ple %batch( chro*atography. chro*atography. ,t cannot pro!ide any separation or purification that cannot be done by a si*ple colu*n purification. The process is rather co*plicated. The single ad!antage which it brings to a chro*atographic purification is that it allows the production of large uantities of highly purified *aterial at a dra*atically reduced cost. The cost reductions co*e about as a result of: the use of a s*aller a*ount of chro*atographic separation *edia stationary phase) phase) a continuous and high rate of production) and decreased sol!ent and energy reuire*ents. This i*pro!ed econo*ic perfor*ance is brought about by a !al!e$and$colu*n arrange*ent that is used to lengthen the stationary phase indefinitely and allow !ery high solute loadings to the process. ,n the con!entional *o!ing bed techniue of production chro*atography the feed entry and the analyte reco!ery are si*ultaneous and continuous) but because of practical difficulties with a continuously *o!ing bed) si*ulated *o!ing bed techniue was proposed. ,n the si*ulated *o!ing bed techniue instead of *o!ing the bed) the feed inlet) the sol!ent or eluent inlet and the desired product exit and undesired product exit positions are *o!ed continuously) gi!ing the i*pression of a *o!ing bed) with continuous flow of solid particles and continuous flow of liuid in the opposite direction of the solid particles. True rue *o!i *o!ing ng bed bed chro chro*at *atog ogra raph phy y %T/ %T/C( C( is only only a theo theoret retica icall conc concep ept. t. ,ts ,ts si*ulation) &/C is achie!ed by the use of a *ultiplicity of colu*ns in series and a co*plex 5
Types Of Reactors !al!e arrange*ent) which pro!ides for flow of the feed *ixture and sol!ent) and eluent eluent or desorbent feed at any colu*n. The !al!ing and piping arrange*ents and the predeter*ined control of these allow switching at regular inter!als the sa*ple entry in one direction) the sol!ent entry in the sa*e direction but at a different location in the continuous loop) whilst changi changing ng the fast produc productt and slow produc productt takeof takeofff positio positions ns to also *o!e *o!e in the sa*e sa*e direction) but at different relati!e locations within the loop.
dantages! &/ &/ pro! pro!id ides es lowe lowerr prod produc ucti tion on cost cost by reu reuiri iring ng less less colu colu*n *n !olu !olu*e) *e) less less chro*atogra chro*atographic phic separation *edia %packing %packing or stationary stationary phase() using less sol!ent sol!ent and less energy) and reuiring far less labor. +t indust industrial rial scale scale an &/ chro*a chro*atog tograp raphic hic separat separator or is operate operated d contin continuou uously sly)) reuiring less resin and less sol!ent than batch chro*atography. The continuous operation facilitates operation control and integration into production plants. ;ow eluent consu*ption 0igh product concentration 0igh producti!ity Continuous process This syste* is useful in the supercritical fluid extraction to obtain large uantity of specific product.
pplications! ,n si#e exclusion chro*atography) chro*atography) where the separation process is dri!en by entropy entropy)) it is not possible to increase the resolution attained by a colu*n !ia te*perature or sol!ent gradients. Conseuently) these separations often reuire &/) to create usable retention ti*e differences between the *olecules or particles being resol!ed. &/ is also !ery useful in the phar*aceutical industry) industry) where resolution of *olecules ha!ing different chirality *ust be done on a !ery large scale. For the purification of fructose fructose)) e.g. in high fructose corn syrup syrup)) or a*ino$acids) a*ino$acids) biological$acid biological$acids) s) etc. on an industrial scale si*ulated *o!ing bed chro*atography is used.
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Types Of Reactors . *luidi *luidi+ed +ed bed bed rreac eactor tor + fluidi#ed bed reactor %F/'( is a type of reactor de!ice de!ice that can be used to carry out a !ariety of *ultiphase che*ical *ultiphase che*ical reactions. ,n this type of reactor) a fluid %gas fluid %gas or liuid( is passed through a solid granular *aterial %usually *aterial %usually a catalyst a catalyst possibly possibly shaped as tiny spheres( at high enough !elocities enough !elocities to to suspend the solid and cause it to beha!e as though it were a fluid. This process) known as fluidi#ation) fluidi#ation) i*parts *any i*portant ad!antages to the F/'. +s a result) the fluidi#ed bed reactor is now used in *any industrial applications.
asic principles! The solid substrate %the catalytic *aterial upon which che*ical species react( *aterial in the fluidi#ed bed reactor is typically supported by a porous a porous plate) plate) known as a distributor. <1= The fluid is then forced through the distributor up through the solid *aterial. +t lower fluid !elocities) the solids re*ain in place as the fluid passes through the !oids in the *aterial. This is known as a packed a packed bed reactor. +s the fluid !elocity is increased) the reactor will reach a stage where the force of the fluid on the solids is enough to balance the weight of the solid *aterial. This stage is known as incipient fluidi#ation and occurs at this *ini*u* fluidi#ation !elocity. 6nce this *ini*u* !elocity is surpassed) the contents of the reactor bed begin to expand and swirl around *uch like an agitated tank or boiling pot of water. The reactor is now a fluidi#ed bed. epending on the operating conditions and properties of solid phase !arious flow regi*es can be obser!ed in this reactor.
dantages! The increase in fluidi#ed bed reactor use in today>s industrial world is largely due to the inherent ad!antages of the technology. technology. ?nifor* article ixing: ue to the intrinsic fluid$like beha!ior of the solid *aterial) fluidi#ed beds do not experience poor *ixing as in packed beds. This co*plete *ixing allows for for a unifo unifor* r* prod produc uctt that that can can ofte often n be hard hard to achi achie! e!ee in othe otherr react reactor or desi design gns. s. The The eli*inat eli*ination ion of radial radial and axial axial concen concentrat tration ion gradients also allows allows for better better fluid$ fluid$sol solid id contact) which is essential for reaction efficiency and uality. ?nifor* ?nifor* Te*perature e*perature @radients: @radients: any che*ical che*ical reactions reactions reuire the addition addition or re*o!al of heat. ;ocal hot or cold spots within the reaction bed) often a proble* in packed beds) are a!oided in a fluidi#ed situation such as an F/'. ,n other reactor types) these local te*perature differences) especially hotspots) can result in product degradation. Thus F/'s are are well well suit suited ed to exother*ic reactio reactions. ns. 'esearc 'esearcher herss ha!e ha!e also learned learned that that the bed$to bed$to$$ surface heat transfer coefficients for F/'s are high. +bility to 6perate 'eactor in Continuous &tate: The fluidi#ed bed nature of these reactors allows for the ability to continuously withdraw product and introduce new reactants into the reaction !essel. 6perating at a continuous process state allows *anufacturers to produce their !arious products *ore efficiently due to the re*o!al of startup conditions in batch in batch processes.
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Types Of Reactors -isadantages! +s in any design) the fluidi#ed bed reactor does ha!e it draw$backs) which any reactor designer *ust take into consideration. ,ncreased 'eactor Aessel &i#e: /ecause of the expansion of the bed *aterials in the reactor) a larger !essel is often reuired than that for a packed bed reactor. This larger !essel *eans that *ore *ust be spent on initial capital costs. u*ping u*ping 'euire*ents 'euire*ents and ressure ressure rop: The The reuire*ent reuire*ent for the fluid to suspend the solid *aterial necessitates that a higher fluid !elocity is attained in the reactor. ,n order to achie!e this) *ore pu*ping power and thus higher energy costs are needed. ,n addition) the pressure the pressure drop associated drop associated with deep beds also reuires re uires additional pu*ping power. #article ntrainment! ntrainment! The high gas !elocities present present in this style of reactor often result in fine particles beco*ing entrained in entrained in the fluid. These captured particles are then carried out of the reactor with the fluid) where they *ust be separated. This can be a !ery difficult and expensi!e proble* to address depending on the design and function of the reactor. This *ay often continue to be a proble* e!en with other entrain*ent reducing technologies.
;ack of Current Current ?nderstandi ?nderstanding: ng: Current Current understanding understanding of the actual beha!ior of the *aterials in a fluidi#ed bed is rather li*ited. ,t is !ery difficult to predict and calculate the co*plex *ass and heat flows within the bed. ue to this lack of understanding) a pilot plant for plant for new processes is reuired. !en with pilot plants) the scale$up can be !ery difficult and *ay not reflect what was experienced in the pilot trial. rosion of ,nternal Co*ponents: The fluid$like beha!ior of the fine solid particles within the bed e!entually results in the wear of the reactor !essel. This can reuire expensi!e *aintenance and upkeep for the reaction !essel and pipes. ressure ressure ;oss &cenarios: &cenarios: ,f fluidi#ation fluidi#ation pressure is suddenly suddenly lost) the surface area of the bed *ay be suddenly reduced. This can either be an incon!enience %e.g. *aking bed restart difficult() or *ay ha!e *ore serious i*plications) such as runaway reactions %e.g. for exother*ic reactions in which heat transfer is suddenly restricted(.
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