Plug reactor

Dump fill, instantaneous addition of waster water into the reactor is rarely used in the field but is implemented practically by including a static fill in the operating strategy. The mathematical representation for the SBR with dump fill is the same as that for the plug reactor at steady state, where the hydraulic residence time in the PFR compares to the time for react in the SBR. 

Neutralizing acids created during processing can cause the formation of salts that can plug reactor components. 

Transfer of the theoretical results obtained for isothermal conditions to the non-isothermal case is rather simple provided the temperature dependencies of the constants are known. A theoretical analysis of non-isothermal processes may be limited by thermal runaway, which is equivalent to the thermal instability already thoroughly studied for chemical reactors.80,81 There are two limiting situations, known as the Semenov and Frank-Kamenetzky models 80,82 these correspond to periodic ideal stirred and periodic ideal plug reactors, respectively. 

There are some fundamental investigations devoted to analysis of the flow in tubular polymerization reactors where the viscosity of the final product has a limit (viscosity < >) i.e., the reactive mass is fluid up to the end of the process. As a zero approximation, flow can be considered to be one-dimensional, for which it is assumed that the velocity is constant across the tube cross-section. This is a model of an ideal plug reactor, and it is very far from reality. A model with a Poiseuille velocity profile (parabolic for a Newtonian liquid) at each cross-section is a first approximation, but again this is a very rough model, which does not reflect the inherent interactions between the kinetics of the chemical reaction, the changes in viscosity of the reactive liquid, and the changes in temperature and velocity profiles along the reactor. 

In a number of works on the analysis of the P(Q) dependence for polymerization plug reactors [24. 26, 27], it was shown that all imlicated reasons for the appearance of non-monotony of the P(Q) dependence may act jointly or independently, resulting in composite and complicated pressure drop—flow rate curves. Even the aj arance of one more pair of extrema on the P(Q) curve (Fig. 8) complicates significantly the prob-... 

A few words on the stability of steady states of polymerization. This question arises immediately as soon as the multiplicity of steady-state conditions spears. It is well known that three solutions are possible in the flow of reactants. The general theory of thermal instability of reactors has been developed in detail in Refe. [16-20,30,31], and the theory of kinetic instability caused by peculiarities of the kinetic schenK (self-acceleration. gel-effect, etc. in Refs. [37-40]). The instability of steady states of poly-nKiization plug reactors of a hydrodynamic nature is more interesting for the present paper. It can be assumed that the state corresponding to the negative slopes of the P(Q) curve are unstable if P = const is maintained [30, 33, 34]. At Q = const, all states are stable and realizable. The analysis of this problem in zero-dimensional formulation [41], for a reactor determined by only one value of T, p, q and a complex variable hydrodynamic resistance has shown that the slope of the curve is not an exhaustive stability criterion. 

T-2—H-1 to T-2—H-8 Graphite Plugs - Reactor Structure Shieldinr Facility Arrangement HR-1 and 2 - Rabbit Tubes HR-3 and 4 - Rabbit Tubes... 

Nevertheless, the blast furnace is an instructive example to examine the question of to what extent this reactor can be regarded as an ideal plug reactor. As deduced in Section 4.10.5.1, we need the residence time distribution, which was measured in 1969 by a pulse experiment with the injection of Kr into the blast air (Standish and Polthier, 1975, see also Levenspiel, 1999). Figures 6.5.22 and 6.5.23 give the dimensions of the blast furnace and the experimental results. 

Multiple reactions in parallel producing byproducts. Consider again the system of parallel reactions from Eqs. (2.16) and (2.17). A batch or plug-flow reactor maintains higher average concentrations of feed (Cfeed) than a continuous well-mixed reactor, in which the incoming feed is instantly diluted by the PRODUCT and... 

In general terms, if the reaction to the desired product has a higher order than the byproduct reaction, use a batch or plug-flow reactor. If the reaction to the desired product has a lower order than the byproduct reaction, use a continuous well-mixed reactor. 

Keep both Cpeedi and Cpeed2 high (i.e., use a batch or plug-flow reactor). 

The series byproduct reaction requires a plug-flow reactor. Thus, for the mixed parallel and series system above, if... 

But what is the correct choice a byproduct reaction calls for a continuous well-mixed reactor. On the other hand, the byproduct series reaction calls for a plug-flow reactor. It would seem that, given this situation, some level of mixing between a plug-flow and a continuous well-mixed reactor will give the best... 

A series combination of plug-flow and continuous well-mixed reactors (Fig. 2.3c and d)... 

Polymerization reactions. Polymers are characterized by the distribution of molecular w eight about the mean as well as by the mean itself. The breadth of this distribution depends on whether a batch or plug-flow reactor is used on the one hand or a continuous well-mixed reactor on the other. The breadth has an important influence on the mechanical and other properties of the polymer, and this is an important factor in the choice of reactor. 

Solution We wish to avoid as much as possible the production of di- and triethanolamine, which are formed by series reactions with respect to monoethanolamine. In a continuous well-mixed reactor, part of the monoethanolamine formed in the primary reaction could stay for extended periods, thus increasing its chances of being converted to di- and triethanolamine. The ideal batch or plug-flow arrangement is preferred, to carefully control the residence time in the reactor. 

Another possibility to improve selectivity is to reduce the concentration of monoethanolamine in the reactor by using more than one reactor with intermediate separation of the monoethanolamine. Considering the boiling points of the components given in Table 2.3, then separation by distillation is apparently possible. Unfortunately, repeated distillation operations are likely to be very expensive. Also, there is a market to sell both di- and triethanolamine, even though their value is lower than that of monoethanolamine. Thus, in this case, repeated reaction and separation are probably not justified, and the choice is a single plug-flow reactor. 

Because the characteristic of tubular reactors approximates plug-flow, they are used if careful control of residence time is important, as in the case where there are multiple reactions in series. High surface area to volume ratios are possible, which is an advantage if high rates of heat transfer are required. It is sometimes possible to approach isothermal conditions or a predetermined temperature profile by careful design of the heat transfer arrangements. 

The performance of fluidized-bed reactors is not approximated by either the well-stirred or plug-flow idealized models. The solid phase tends to be well-mixed, but the bubbles lead to the gas phase having a poorer performance than well mixed. Overall, the performance of a fluidized-bed reactor often lies somewhere between the well-stirred and plug-flow models. 

Continuous well-mixed reactors to plug-flow... 

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