In chemical engineering the name cstr is often used to refer to an idealised agitated tank reactor used to model operation variables required to attain a specified output. Continuously stirred tank reactor cstr run at steady state with continuous flow of reactants and products. They may be used by themselves, in series, or in a battery. Most homogeneous liquid phase reactions employs cstr. May 21, 2015 a continuous flow reactor, the feed to reactor and the discharge from it are continuous. Another type of reactor used in industrial processes is the plug flow reactor pfr. Apr 05, 2017 to learn more about plug flow reactors, visit the visual encyclopedia of chemical engineering. A continuous stirred tank reactor cstr is a batch reactor equipped with an impeller or other mixing device to provide efficient mixing. The main assumption in this case is that the concentration of the incoming fluid will become.
The key assumption is that as a plug flows through a pfr, the fluid is perfectly mixed in the radial direction but not in the axial direction forwards or backwards. Approach to steady state in a continuous stirred tank reactor cstr. A cstr often refers to a model used to estimate the key unit operation variables when using a continuous agitated. A comparison of the performance of single cstr and 2cstr systems against a stirred batch immobilized enzyme ime reactor has been made. A continuous stirred tank reactor cstr is a wellmixed vessel that operates at steadystate qinqoutq. A plug flow reactor, and continuous stirred tank reactor. In this chapter, design of continuous stirred tank reactor will be discussed. Continuous stirred tank reactors are used very commonly in industrial processes. This problem can be managed by breaking up the reactor into a series of mixed stages separated by small plug flow channels. Continuous stirred tank reactor cstr is the most generally employed bioreactor for biohydrogen production in continuous mode because of its simplicity in configuration, easy functioning, efficient uniform stirring, and proper maintenance of temperature and ph fig. Common industrial uses of tubular reactors are in gasoline production, oil cracking, synthesis of ammonia from its elements, and the oxidation of sulfur dioxide to sulfur trioxide. Cstr a continuous stirred tank reactor cstr is a vessel to which reactants are added and products removed while the contents within the vessel are vigorously stirred using internal agitation or by internally or externally recycling the contents.
Development of a continuous process for enol esters of. The three main reactor types developed thus far batch, continuousstirredtank, and plugflow reactors are useful for modeling many complex chemical reactors. A raceway pond can be modeled as a plug flow reactor pfr, but if the recirculation rate is much higher than the dilution rate, it can be approximated as a continuous stirred tank reactor cstr gomez et al. Design strategy and process optimization for reactors with. A batch reactor has no input or output when the reaction is occurring fa0 fa 0, so. Continuous flow reactors are almost always operated at steady state. In theory, any sample taken from the overflow of the reactor will be identical with. Reactor theory and practice continuous flow stirred tank reactor cfstr a continuous flow stirred tank reactor cfstr is one in which the contents are stirred so uniformly that it is assumed that no variation or concentration gradients exist within the vessel. It is referred to as the continuousstined tankreactor cstr or vat, or backmix reactor, and is primarily used for. Continuous reactors alternatively referred to as flow reactors carry material as a flowing stream. It was operated full at all times, as flow enters at the bottom and exits at the top. Continuous reactors cstr plug flow reactor tubular flow reactor 26. Pdf residence time distribution of a tubular reactor.
To improve understanding it is useful to study ideal reactors first. Continuous stirred tank reactors cstrs type of reactor. Continuous stirredtank reactors are most commonly used in industrial processing, primarily in homogeneous liquidphase flow reactions, where constant agitation is required. Cstr continuous stirred tank reactor and the pfr plug flow reactor. The main assumption in this case is that the concentration of the incoming fluid will become instantaneously equal to the outgoing upon entering the vessel. Up to this point we have neglected a careful treatment of the fluid flow pattern within the reactor. Given r a as a function of conversion, one can size any type of reactor. To learn more about plug flow reactors, visit the visual encyclopedia of chemical engineering. Continuous stirred tank reactors chemical engineering. Each pond model includes the mass balances for the main metabolites and an estimate of the variation of the average light. The residence time is calculated by dividing the volume of the tank by the average volumetric flow rate.
A 2 l batchcontinuously stirred tank reactor and 900 ml stainless steel pfr are used for benchmark kinetic studies. The most familiar form of continuous reactor of this type is the continuously stirred tank reactor cstr. They are used most frequently with liquid phases, but can handle gas or solid reactions as well. Reactors jordan university of science and technology. The fluid mixing characteristics are rather sensitive to the scale of the reactor. Tubular reactor plug flow cell culture bioreactors 3 in general, laboratory and small pilot plant bioreactors are used for process development and optimization. Detailed physical descriptions of these reactors can be found in both the professional reference shelf prs for chapter 1 and in the visual encyclopedia of. General material balance of reacting system batch reactor. In theory, any sample taken from the overflow of the reactor will be identical with any sample taken from within the vessel. Cstr pfr manual continuous stirred tank reactor and.
Plug flow reactors pfrs another type of reactor used in industrial processes is the plug flow reactor pfr. Units are the vessels or basin that holds wastewater for the treatment by chemical or biological processes. Continuousflow stirred tank reactor cstr a reaction vessel in which the feed is continuously added and the products continuously removed. For this type of reactor, mixing is complete, so that the temperature and the composition of the reaction mixture. Like the cstrs, a constant flow of reactants and products and exit the reactor. Vessel used for chemical reaction that has no feed or effluent. To achieve this, the batch reactor available at the unit operation laboratory department of chemical engineering, university of khartoum had been repaired and modified to suit the experimental procedures. For a simple reaction of positive order, a comparison between a. For this type of reactor, mixing is complete, so that the temperature and the composition of the reaction.
Reactors are usually designed based on rate considerations. The residence time is calculated by dividing the volume of. Continuous isothermal laboratory reactors can be compared to two ideal extremes. The output of the first tank is the input of the second tank. Most flow reactors are neither ideal plug flow nor continuous stirred tank reactors. Therefore, plug flow reactor is rarely used for large scale operation of cell cultivation. Depending upon the flow and operating conditions and the methods of mixing of the wastewater therein, the reactors have the following main types. When the downtimes in a batch reactor are not too small, the 2cstr system may become attractive and therefore a proper consideration should be given to the 2cstr system particularly when the application of a plug flow reactor is not practicable.
These reactors provide enough residence time for the reaction to take place with satisfactory conversion. Experiment 3 saponification of ethyl acetate and sodium. Apr 05, 2017 reactors continuous stirred tank reactor. This makes it difficult in accounting for actual conversion obtained from such reactors thus causing much.
In such reactors, the reaction rate expression must be known determined. Plug flow reactor an overview sciencedirect topics. At time zero we start adding a small flow of a tracer to the feed stream and measure the tracer concentration in the effluent stream. The continuous stirredtank reactor cstr has been commonly used in syngas fermentations. Compared with conventional reactor types, such as the continuous stirredtank reactor and the fixed. A comparative study of saponification reaction in a pfr. The plug flow reactor model pfr, sometimes called continuous tubular reactor, ctr is normally the name given to a model used in chemical engineering to describe chemical reactions in continuous, flowing systems of cylindrical geometry. Continuously stirred tank reactor cstr arranged as one long reactor or many short reactors in a tube bank. The volume of a pfr can be represented as the shaded area in the levenspiel plot shown below. This experiment was conducted to study the saponification reaction between sodium. Furthermore, plugflow bioreactors are intrinsically more. Jan 05, 2015 continuous reactors cstr plug flow reactor tubular flow reactor 26.
Furthermore, plug flow bioreactors are intrinsically more. A continuous stirred tank reactor cstr is a continuous reactor that runs at a steady state. Applications of plug flow reactor plug flow reactors have a wide variety of applications in either gas or liquid phase systems. The continuous stirred tank reactor cstr, also known as vat or backmix reactor, or a continuous flow stirred tank reactor cfstr, is a common model for a chemical reactor in chemical engineering and environmental engineering. A continuous flow reactor, the feed to reactor and the discharge from it are continuous. Figure shows continuous stirred tank reactors, a with agitator and internal heat transfer surface, b with pump around mixing and external heat transfer surface. The continuousstirred tank reactor cstr involves feeding. Continuous stirred tank reactor an overview sciencedirect topics. The pfr model is used to predict the behavior of chemical reactors of such design, so that key reactor variables, such as the dimensions of the reactor, can be estimated. Unsteadystate condition c co although the material is nonreactive. The model also gives a prediction of the number of ideal continuous stirred tank reactors cstr that could represent the nonideal plug flow reactor pfr in question.
Abstract this experiment involves a continuous stirred tank reactor cstr in series. Cstrs are also used in the pharmaceutical industry as a loop reactor. Plug flow reactor model advantages and disadvantages. A steady state must be reached where the flow rate into the reactor equals the flow rate out, for otherwise the tank would empty or overflow. These reactors are the batch reactor br, the plug flow reactor pfr and the continuous stirred tank reactor cstr. The vessel tank is continuously stirred to maintain a uniform concentration within the vessel. Continuous stirred tank reactors cstrs mit opencourseware. Rather, a stirred tank or other mixing vessel type of reactors with a continuous supply of oxygen from the gas phase by air sparging, are frequently used. Compared with batch reactor systems, hydrogenproducing bacteria in a cstr are well suspended in mixed liquor and suffer less from mass transfer resistance. It is a tubular reactor, typically long with a small cross sectional area. A comparative study of saponification reaction has been conducted in a continuous stirred tank reactor cstr and plug flow reactor pfr.
The concentration is kept uniform for each reactor and it is observed that there is a change in concentration as fluids move from one reactor to the other reactor. The pfr model is used to predict the behaviour of chemical reactors of tubular design, so that key reactor. In this lecture we explore some of the limits of this. The three types of continuous flow reactor are plug flow reactor, the dispersed plug flow reactor, and completely mixed or continuously stirred tank reactors cstrs. A photo and schematic of the reactor and its associated. We expect to see a continuous change in the concentration of the effluent stream until, after a long time, it matches the concentration of the feed stream. In these types of bioreactors, biohydrogen generating microbial population is entirely circulated and is in suspension. Reactants are continuously fed into the reactor and emerge as continuous stream of product. Continuous stirred tank reactor an overview sciencedirect. The batch reactor, the continuous stirredtank reactor, and the plugow reactor.
In a cstr, syngas is continuously injected into the reactor through a gas diffuser, while large gas bubbles dispersed in the fermentation broth are immediately broken into smaller ones by mechanical agitation, enabling the gaseous substrates to be more accessible to microbes. Continuousflow stirred tank reactor cfstr or completelymix reactor. Cstr design equations space time and space velocity concept. Cstr consists of a stirred tank that has a feed stream and discharge stream. The plug flow reactor model pfr, sometimes called continuous tubular reactor, ctr, or piston flow reactors is a model used to describe chemical reactions in continuous, flowing systems of cylindrical geometry. This is essentially a batch reactor used in a continuous flow. Continuousflow reactors continuous stirred tank reactor cstr 0, 1 nr i i i ki v k r k dn f f r v dt q we need suplementary information state behavior of reaction mixture startup shutdown molar flow rates of individual species 1 0 1, volume of reactor n ki i i i r a k nr nt v const q molar balance of species i overall. Instead, chemical species are flowed along a tube as a plug, as shown in figure 25. Cstr and a plug flow reactor reveals the superiority of the latter.
Continuous reactors are used for a wide variety of chemical and biological processes within the food, chemical and pharmaceutical industries. Each plug of differential volume is considered as a separate entity, effectively an infinitesimally small continuous stirred tank reactor, limiting to zero volume. In pfrs, however, the reactor contents are not continuously stirred. Plug flow reactors and comparison to continuously stirred tank reactors. Reactor choice is mainly possible when building a new plant or in certain cases of retrofitting an existing one. The maintenance of the reactor includes change of bearing and bushes. Q8, mixing problem, continuously stirred tank reactor, cstr. Continuous stirred tank reactors are most commonly used in industrial processing, primarily in homogeneous liquidphase flow reactions, where constant agitation is required.
Plug flow reactor model advantages and disadvantages advantages and disadvantages cstrs continuous stirred tank reactor and pfrs have fundamentally different equations, so the kinetics of the reaction being undertaken will to some extent determine which system should be used. A raceway pond can be modeled as a plug flow reactor pfr, but if the recirculation rate is much higher than the dilution rate, it can be approximated as a continuous stirredtank reactor cstr gomez et al. The reaction chosen for investigation was hydrolysis of ethyl acetate with sodium hydroxide. Figure 9 a line diagram illustrating a continuous stirred tank reactor. Continuous flow stirred tank reactor cstr a reaction vessel in which the feed is continuously added and the products continuously removed. Tracer studies in a series system of continuous stirred. Two commonly used reactors are the cstr continuous stirred tank reactor and the pfr plug flow reactor. Continuous stirred tank reactor and plug flow reactor manual this unit operations experiment was made possible by equipment donations from the richard braatz research group and pfr design by ryan mcgowan. The batch reactor, the continuous stirred tank reactor, and the plug ow reactor. The integral to calculate the pfr volume can be evaluated using a method such as simpsons onethird rule pg 925. Reactor size comparisons for pfr and cstr this lecture covers reactors in series and in parallel, and how the choice of reactor affects selectivity versus conversion. Chemical reactions in a reactor are either exothermic or endothermic and require that energy can.