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{{Chemical engineering}}
In [[chemical engineering]],A '''chemical reactorsreactor''' areis vesselsan designedenclosed tovolume containin which a [[chemical reaction]] takes place.<ref>{{Cite book|url=https://www.worldcat.org/oclc/191805887|title=Perry's chemical engineers' handbook. Section Also19, referredReactors|last=Joseph.|first=Pereira, toCarmo|date=2008|publisher=McGraw-Hill|others=Leib, asTiberiu aM.|year=|isbn=9780071542265|edition=8th reactioned|location=[New vesselYork]|pages=4|chapter=19|oclc=191805887}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=XuSq2qtbp60C&pg=PA109|title=Flows of Reactive Fluids|last=Prud'homme|first=Roger|date=2010-07-15|publisher=Springer Science & Business Media|year=|isbn=9780817646592|location=|pages=109|language=en}}</ref> In [[chemical engineering]], theit reactantsgenerally containedunderstood areto substancesbe thata changeprocess formvessel afterused to carry out a chemical reaction.,<ref>{{Cite newsbook|url=https://wwwbooks.highpuritygoogle.com/industries/bio-pharmaceutical/sanitary-dip-tubes/books?id=94EqBgAAQBAJ&pg=PA67|title=SanitaryGreen DipChemical TubesEngineering: -An HighIntroduction Purityto SystemsCatalysis, Inc.|newspaper=HighKinetics, Purityand Systems,Chemical IncProcesses|last=Suresh|first=S.|languagelast2=en-USSundaramoorthy|first2=S.|access-date=20162014-1012-1918|publisher=CRC Press|year=|isbn=9781466558854|location=|pages=67|language=en}}</ref> One examplewhich is aone of the classic [[pressureUnit reactoroperation|unit operations]]. in chemical process analysis. The design of a chemical reactor deals with multiple aspects of [[chemical engineering]]. Chemical engineers design reactors to maximize [[net present value]] for the given reaction. Designers ensure that the reaction proceeds with the highest efficiency towards the desired output product, producing the highest [[yield (chemistry)|yield]] of product while requiring the least amount of money to purchase and operate. Normal [[operating expense]]s include energy input, energy removal, [[raw material]] costs, labor, etc. Energy changes can come in the form of heating or cooling, pumping to increase pressure, frictional pressure loss (such as pressure drop across a 90° elbow or an [[orifice plate]]) or agitation.
 
[[Chemical reaction engineering]] is the branch of chemical engineering which deals with chemical reactors and their design, especially by application of [[chemical kinetics]] to industrial systems.
[[Image:Batch reactor.2.jpg|thumb|left|180px|Cut-away view of a stirred-tank chemical reactor with a cooling jacket]]
[[Image:Final half coil vessel.JPG|thumb|left|180px|Chemical reactor with half coils wrapped around it]]
The most common basic types of chemical reactors are tanks (where the reactants mix in the whole volume) and pipes or tubes (for [[laminar flow reactor|laminar flow reactors]] and [[Plug flow reactor|plug flow reactors]])
There are a couple of main basic vessel types:
*A tank
*A pipe or tubular reactor ([[laminar flow reactor]](LFR))
Both types can be used as continuous reactors or batch reactors, and either may accommodate one or more solids ([[reagent]]s, [[catalyst]], or inert materials), but the reagents and products are typically fluids. Most commonly, reactors are run at [[steady-state (chemical engineering)|steady-state]], but can also be operated in a [[Transient state (chemical engineering)|transient state]]. When a reactor is first brought into operation (after maintenance or inoperation) it would be considered to be in a transient state, where key process variables change with time.
 
Both types can be used as continuous reactors or batch reactors, and either may accommodate one or more solids ([[reagent]]s, [[catalyst|catalysts]], or inert materials), but the reagents and products are typically fluids (liquids or gases). Reactors Mostin commonly,[[Continuous reactorsprocess|continuous processes]] are typically run at [[steady-state (chemical engineering)|steady-state]], butwhereas canreactors alsoin [[Batch production|batch processes]] are benecessarily operated in a [[Transient state (chemical engineering)|transient state]]. When a reactor is first brought into operation, (aftereither maintenancefor orthe inoperation)first ittime wouldor beafter considereda toshutdown, beit is in a transient state, whereand key [[Process variable|process variables]] change with time.
There are three main basic models used to estimate the most important process variables of different chemical reactors:
* [[Batch reactor|''Batch reactor'' model (batch)]],
* [[Continuous stirred-tank reactor model|''Continuous stirred-tank reactor'' model (CSTR)]], and
* [[Plug flow reactor model|''Plug flow reactor'' model (PFR)]].
 
There are three main basicidealised models used to estimate the most important process variables of different chemical reactors:
Furthermore, catalytic reactors require separate treatment, whether they are batch, CST, or PF reactors, as the many assumptions of the simpler models are not valid.
* [[Batch reactor|''Batch reactor'' model (batch)]],
* [[Continuous stirred-tank reactor model|''Continuous stirred-tank reactor'' model (CSTR)]], and
* [[Plug flow reactor model|''Plug flow reactor'' model (PFR)]].
 
Many real-world reactors can be modeled as a combination of these basic types.
Key process variables include
 
* Residence time (τ, lower case Greek tau)
Key process variables include:
* [[Residence time (fluid dynamics)|Residence time]] (τ, lower case Greek tau)
* Volume (V)
* Temperature (T)
* Concentrations of chemical species (C<sub>1</sub>, C<sub>2</sub>, C<sub>3</sub>, ... C<sub>n</sub>)
* Heat transfer coefficients (h, U)
* Chemical reactor manufacturer <ref>{{cite web|last1=qin|first1=su|title=Chemical reactor manufacturer|url=nhjct.com|website=JCT Machinery}}</ref>(h, U)
 
A chemical reactor, typically tubular reactor, couldcan often be a [[packed bed]]. In Typicalthis packedcase, bedthe reactorstube consistor ofchannel acontains chamber,particles suchor aspellets, usually a tubesolid or[[Catalysis|catalyst]].<ref>{{Cite channelbook|url=https://books.google.com/books?id=hhHABAAAQBAJ&pg=PA1057|title=Chemical thatReactor containsModeling: catalystMultiphase particlesReactive orFlows|last=Jakobsen|first=Hugo pellets,A.|date=2014-04-02|publisher=Springer andScience a& Business Media|year=|isbn=9783319050928|location=|pages=1057|language=en}}</ref> The reactants, in liquid thator flowsgas phase, are pumped through the catalyst bed.<ref>{{Cite web|url=https://www.comsol.com/blogs/packed-bed-reactor/|title=What Is a Packed Bed Reactor?|website=COMSOL Multiphysics©|access-date=2016-10-19}}</ref> A chemical reactor may also be a [[fluidized bed]]; see [[Fluidized bed reactor]].
 
Chemical reactions occurring in a reactor may be [[exothermic]], meaning giving off heat, or [[endothermic]], meaning absorbing heat. A chemicaltank reactor vessel may have a cooling or heating jacket or cooling or heating coils (tubes) wrapped around the outside of its vessel wall to cool down or heat up the contents, while tubular reactors can be designed like [[Heat exchanger|heat exchangers]] if the reaction is strongly [[Exothermic process|exothermic]], or like [[Furnace|furnaces]] if the reaction is strongly [[Endothermic process|endothermic]].<ref>{{Cite book|url=https://books.google.com/books?id=MYWfHbLnDY4C&pg=PA8|title=Chemical Engineering, Volume 3: Chemical and Biochemical Reactors and Process Control|last=Peacock|first=D. G.|last2=Richardson|first2=J. F.|date=2012-12-02|publisher=Elsevier|year=|isbn=0080571549|location=|pages=8|language=en}}</ref>
 
==Types==
===Batch reactor===
{{Main|Batch reactor}}
The simplest type of reactor is a batch reactor. Materials are chargedloaded ininto a batch reactor, and the reaction proceeds with time. A batch reactor does not reach a steady state, and control of temperature, pressure and volume is often necessary. Thus, aMany batch reactorreactors therefore hashave ports for sensors and material input and output. Batch reactors are typically used in small-scale production and reactions with biological materials, such as in brewing, pulping and production of enzymes. One example of a batch reactor is a [[pressure reactor]].
 
===CSTR (continuous stirred-tank reactor)===
[[Image:Chemical reactor CSTR AISI 316.JPG|thumb|350px|right|Checking condition inside the case of a [[continuous stirred tank reactor]] (CSTR). Note the [[impeller]] (or agitator) blades on the shaft for [[Mixing (process engineering)|mixing]].
Also note the [[Baffle (in vessel)|baffle]] at the bottom of the image which also helps in mixing.]]
In a CSTR, one or more fluid reagents are introduced into a tank reactor (which is typically) equippedstirred with an [[impeller]] whileto theensure reactorproper effluentmixing is removed. The impeller stirsof the reagents towhile ensurethe properreactor [[Mixingeffluent (processis engineering)|mixing]]removed. Simply dividingDividing the volume of the tank by the average [[volumetric flow rate]] through the tank gives the ''[[Space time (chemical engineering)|space time'']], or the averagetime amountrequired ofto timeprocess aone discretereactor quantityvolume of reagent spends inside the tankfluid. Using [[chemical kinetics]], the reaction's expected [[percent]] completion can be calculated. Some important aspects of the CSTR:
* At steady-state, the mass flow rate in must equal the mass flow rate out, otherwise the tank will overflow or go empty (transient state). While the reactor is in a transient state the model equation must be derived from the differential mass and energy balances.
* The reaction proceeds at the reaction rate associated with the final (output) concentration, since the concentration is assumed to be homogenous throughout the reactor.
* Often, it is economically beneficial to operate several CSTRs in series. This allows, for example, the first CSTR to operate at a higher reagent concentration and therefore a higher reaction rate. In these cases, the sizes of the reactors may be varied in order to minimize the total [[capital investment]] required to implement the process.
* It can be demonstrated that an [[Infinity|infinite]] number of infinitely small CSTRs operating in series would be equivalent to a PFR.<ref>{{Cite book|url=https://books.google.com/books?id=XicUDgAAQBAJ&pg=PA80|title=Coulson and Richardson’s Chemical Engineering: Volume 3A: Chemical and Biochemical Reactors and Reaction Engineering|last=Ravi|first=R.|last2=Vinu|first2=R.|last3=Gummadi|first3=S. N.|date=2017-09-26|publisher=Butterworth-Heinemann|year=|isbn=9780081012239|location=|pages=80|language=en}}</ref>
The behavior of a CSTR is often approximated or modeled by that of a Continuous Ideally Stirred-Tank Reactor (CISTR). All calculations performed with CISTRs assume [[perfect mixing]]. If the residence time is 5-10 times the mixing time, this approximation is considered valid for engineering purposes. The CISTR model is often used to simplify engineering calculations and can be used to describe research reactors. In practice it can only be approached, particularly in industrial size reactors in which the mixing time may be very large.