Reactor types plug flow tubular

In the three idealized types of reactors just discussed (the perfectly mixed batch reactor, the plug-flow tubular reactor [PFRj), and the perfectly mixed con-tinuous-stirred tank reactor [CSTR]), the design equations (i.e., mole balances) were developed based on reactor volume. The derivation of the design equation for a packed-bed catalytic reactor (PBR) will be carried out in a manner analogous to the development of the tubular de.sign equation. To accomplish this derivation, we simply replace the volume coordinate in Equation (1-10) with the catalyst mass (i.e., weight) coordinate W (Figure 1-14). 

Runaway criteria developed for plug-flow tubular reactors, which are mathematically isomorphic with batch reactors with a constant coolant temperature, are also included in the tables. They can be considered conservative criteria for batch reactors, which can be operated safer due to manipulation of the coolant temperature. Balakotaiah et al. (1995) showed that in practice safe and runaway regions overlap for the three types of reactors for homogeneous reactions (1) batch reactor (BR), and, equivalently, plug-flow reactor (PFR), (2) CSTR, and (3) continuously operated bubble column reactor (BCR). 

For a few highly idealized systems, the residence time distribution function can be determined a priori without the need for experimental work. These systems include our two idealized flow reactors—the plug flow reactor and the continuous stirred tank reactor—and the tubular laminar flow reactor. The F(t) and response curves for each of these three types of well-characterized flow patterns will be developed in turn. 

We will consider only the batch reactor in this chapter. This is a type of reactor that does not scale up well at all, and continuous reactors dominate the chemical industry. However, students are usually introduced to reactions and kinetics in physical chemistry courses through the batch reactor (one might conclude fi om chemistry courses that the batch reactor is the only one possible) so we wiU quickly summarize it here. As we vrill see in the next chapter, the equations and their solutions for the batch reactor are in fact identical to the plug flow tubular reactor, which is one of our favorite continuous reactors so we will not need to repeat all these definitions and derivations in the section on the plug flow tubular reactor. 

Reactor type For the highest relative yield of P a batch or tubular plug-flow reactor should be chosen. If a continuous stirred-tank system is adopted on other grounds, several tanks should be used in series so that the behaviour may approach that of a plug-flow tubular reactor. 

In reactions with parallel steps of different reaction orders or with sequential steps, selectivities depend on the reactor type. Batch and plug-flow tubular reactors give higher selectivities to the product formed by the parallel step of higher order, or to the first product in a step sequence, than do continuous stirred-tank reactors. 

Beyne and Froment [1993] simulated a tubular reactor with plug flow and diffiisional limitations inside the catalyst for the process discussed already in Section 3. The main reaction is of the type A B and coke is formed through a polymerization mechanism from a site covered by coke... 

For each of the chemical species participating in the mechanism, a mass balance equation must be written. The appropriate form of the mass balance for the specific type of reactor at hand must be used. Two of the most common types of reactors used in industry are the CSTR (continuous stirred tank reactor) and the tubular reactor. The corresponding mathematical models for their idealized forms, based on transport phenomena equations and available in any standard chemical reactor text [17, 18], are the ideal CSTR and the ideal model for the plug flow tubular reactor (PFR). The ideal CSTR model is given by Equation 12.1 ... 

Consideration of the basic differences between these scenarii lead to the present proposition that for a multi-stage continuous PHA-production process, the use of a plug-flow tubular reactor, or PFTR (in which Reynolds numbers are large), brings substantial increases in productivity when compared to a system consisting of CSTRs only. Support of this assertion comes firom the works of Levenspiel (29), where mean residence times for the two types of reactors are compared under the restriction of a desired goal ... 

In this chapter the focus is on reactors. First we introduce the general factors that affect the selection of the reactor. In Section 6.2 are given general guidelines. Section 6.3 considers details for different types of reactions that affect the size of the reactor. The rest of the chapter discusses some specifics about the different types of reactor. Section 6.4 considers burners. Plug flow tubular reactors, PFTR, are considered in Sections 6.5 to 6.26. Stirred tanks reactors, STR, are considered in Section 6.27 to 6.33. Finally Sections 6.34 to 6.37 explore combining reactors with other unit operations such as distillation, extmsion, membranes and vacuum pumps. 

Taking into consideration the fact that fast polymerisation processes are characterised by inequality of chemical reaction time and transfer time ( chem < it is clear that an increase of facilitates the decrease of and both these processes are comparable in duration. The increase in linear flow rate V, i.e., the intensification of heat and mass exchange in the system, is equivalent to a slow dovm of the polymerisation reaction itself, compared with the transfer process. Therefore, the conventional approaches to external heat removal, which normally have such a restrictive effect on conventionally designed fast polymerisation processes implemented in stirred tank reactors, play an essential role at both high V and values when quasi-plug flow tubular turbulent reactors are used. In this case, control of the external temperature can be significantly enchanced due to zone-type catalyst loading. 

There are two major types of continuous reactors plug-flow tubular reactor (PFTR) and CSTR. The polymerization kinetics with PFTR is similar to that of batch reactor. In PFTR, the concentrations of reactants and products vary with location but not with time. The rate equations derived for batch processes can be easily transformed into their corresponding equations for PFTR using... 

Example 9.11 Which type of isothermal reactor would produce the narrowest possible distribution of chain lengths in a free-radical addition polymerization continuous stirred tank reactor (CSTR, or backmix), batch (assume perfect stirring in each of the previous), plug-flow tubular, or laminar-flow tubular ... 

Continuous-Flow Stirred-Tank Reactor. In a continuous-flow stirred-tank reactor (CSTR), reactants and products are continuously added and withdrawn. In practice, mechanical or hydrauHc agitation is required to achieve uniform composition and temperature, a choice strongly influenced by process considerations, ie, multiple specialty product requirements and mechanical seal pressure limitations. The CSTR is the idealized opposite of the weU-stirred batch and tubular plug-flow reactors. Analysis of selected combinations of these reactor types can be useful in quantitatively evaluating more complex gas-, Hquid-, and soHd-flow behaviors. 

Another classification refers to the shape of the vessel. In the case of the laboratory vessel installed with a stirrer, the composition and temperature of die reaction is homogeneous in all parts of die vessel. This type of vessel is classified as a stiiTcd tank or well mixed reactor. Where there is no mixing in the direction of flow as in the cylindrical vessel, it is classified as a plug flow or tubular flow reactor. 

There are many chemically reacting flow situations in which a reactive stream flows interior to a channel or duct. Two such examples are illustrated in Figs. 1.4 and 1.6, which consider flow in a catalytic-combustion monolith [28,156,168,259,322] and in the channels of a solid-oxide fuel cell. Other examples include the catalytic converters in automobiles. Certainly there are many industrial chemical processes that involve reactive flow tubular reactors. Innovative new short-contact-time processes use flow in catalytic monoliths to convert raw hydrocarbons to higher-value chemical feedstocks [37,99,100,173,184,436, 447]. Certain types of chemical-vapor-deposition reactors use a channel to direct flow over a wafer where a thin film is grown or deposited [219]. Flow reactors used in the laboratory to study gas-phase chemical kinetics usually strive to achieve plug-flow conditions and to minimize wall-chemistry effects. Nevertheless, boundary-layer simulations can be used to verify the flow condition or to account for non-ideal behavior [147]. 

---