Types of tubular reactor

Homogeneous or homo, catalysed Catalysed on the wall Heterogeneously catalysed  

Mass balance 2 Momentum balance 3 Energy balonce 4 

We may first divide tubular reactors into those designed for homogeneous reactions, and therefore basically just an empty tube, and those designed for a heterogeneously catalyzed reaction, and hence to be packed with a catalyst. Both types can of course be operated adiabatically, and it was the simplest model of these that we discussed in the last chapter. If the temperature of the reactor is to be controlled this is through the wall, and the associated problems of heat transfer now arise. These include transfer at the wall and subsequent radial diffusion across the flowing reactants. In the empty tubular reactor there may be considerable variations in flow rate across the tube. For example, in the slow laminar flow the fluid 

In all these cases, the correct design must grow from the equations of mass, energy, and momentum balance to which we now turn in the next few sections. From these we proceed to the design problem (Sec. 9.5) and hence to elementary considerations of optimal design (Sec. 9.6). The stability and sensitivity of a tubular reactor is a vast and fascinating subject. Since the steady state equations are ordinary differential equations, the equations describing the transient behavior are partial differential equations. This 

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The single-jacketed tube reactor is the simplest type of tubular reactor to conceptualize and to fabricate. It may be used only when the heat transfer requirements are minimal because of the low surface area to volume ratio characteristic of these reactors. 

In this chapter we have discussed the several types of tubular reactors and some important aspects of their steady-state design. In all tubular reactors, the inlet temperature plays a significant role in the design of the reactor system. Higher inlet temperatures result in smaller reactors for the same per-pass conversion, but also result in higher exit temperatures. 

The four types of tubular reactor systems designed in Chapter 5 are investigated for dynamic controllability in this chapter. The four flowsheets are given in Figures 6.1 -6.4 with stream conditions and equipment sizes shown. These are the optimum economic flowsheets for the expensive catalyst cases. A three-bed cold-shot system is shown, but a seven bed system is the optimum steady-state design. As we will show, the seven bed system is uncontrollable. 

The steady-state designs of four types of tubular reactors were illustrated in Chapter 5. Now we want to explore the dynamics and control of each of these reactors. 

Conclusions for Aspen Simulation of Different Types of Tubular Reactors... 

Simulation examples of four types of tubular reactors have been presented in the sections above. The adiabatic and constant-coolant temperature models are easier to set up and seem to run with fewer problems. In the adiabatic reactor the only variable that can be controlled is the inlet temperature. In the cooled reactors a temperature can be controlled by manipulating either the coolant temperature or the coolant flowrate, depending on the model. 

As stated previously, another distinction usually made is between slurry and supported catalyst reactors. In slurry photocatalytic reactors the catalyst is present in the form of small particles suspended in the water being treated. These reactors generally tend to be more efficient than supported catalyst reactors, because the semiconductor particles provide a larger contact surface area per unit mass. In fact, the state of the photocatalyst is important both to increase contaminant adsorption and to improve the distribution of absorbed radiation. In a slurry unit the photocatalyst has a better contact with the dissolved molecules and is allowed to absorb radiation in a more homogeneous manner over the reaction volume. Using suspended catalyst has been the usual practice in PTC, CPC, and other types of tubular reactors. The drawback of this reactor design is the requirement for separation and recovery of the very small particles at the end of the water treatment process. This may eventually complicate and slow down the water throughput. 

Both types of tubular reactors are isothermal in operation and have a temperature vs. methanol concentration profile similar to that shewn in Fig. 

Small tubes are commonly employed where the reaction is rapid and/or the heat of reaction must be removed rapidly. The two conventional types of tubular reactors are (1) coils immersed in a constant-temperature bath and (2) a jacketed pipeline in which the inner tube is designed to withstand the reaction pressure. A modification of the conventional jacketed-pipe reactor can be used where it is desirable to minimize the thickness of the inner tube in order to reduce the area required for heat transfer. An example of this type of equipment is the liquid-phase heat exchanger of the Bureau of Mines, in which the outside pipe has an outside diameter of 4 2 ill- wall thickness of 1.005 in. The outside diameter of the inner tube is in., but the wall thickness is only 0.16 in. The worldng... 

Several types of tubular reactors have been reported. Recirculation loop reactors have a pump which continuously circulates the reacting dispersion through a tube loop with raw materials being introduced at one location and product latex removed at another. Material passing through the pump is remixed with each pass. If the circulation rate is significantly higher than the feed and effluent rates, which is usually the case, the residence time distribution approaches that of a well-mixed CSTR, Hence this reactor cannot be used to produce latexes with narrow PSDs. 

A useful classification of lands of reaclors is in terms of their concentration distributions. The concentration profiles of certain limiting cases are illustrated in Fig. 7-3 namely, of batch reactors, continuously stirred tanks, and tubular flow reactors. Basic types of flow reactors are illustrated in Fig. 7-4. Many others, employing granular catalysts and for multiphase reactions, are illustratea throughout Sec. 23. The present material deals with the sizes, performances and heat effects of these ideal types. They afford standards of comparison. 

Low density polyethylene is made at high pressures in one of two types of continuous reactor. Autoclave reactors are large stirred pressure vessels, which rely on chilled incoming monomer to remove the heat of polymerization. Tubular reactors consist of long tubes with diameters of approximately 2.5 cm and lengths of up to 600 m. Tubular reactors have a very high surface-to-volume ratio, which permits external cooling to remove the heat of polymerization. 

A laminar-flow reactor (LFR) is rarely used for kinetic studies, since it involves a flow pattern that is relatively difficult to attain experimentally. However, the model based on laminar flow, a type of tubular flow, may be useful in certain situations, both in the laboratory and on a large scale, in which flow approaches this extreme (at low Re). Such a situation would involve low fluid flow rate, small tube size, and high fluid viscosity, either separately or in combination, as, for example, in the extrusion of high-molecular-weight polymers. Nevertheless, we consider the general features of an LFR at this stage for comparison with features of the other models introduced above. We defer more detailed discussion, including applications of the material balance, to Chapter 16. 

There is also a wider variety of reactor and system types for tubular reactors. Many operate adiabatically, while others are heated or cooled. Multiple tubular reactors in series with intermediate heating or cooling are quite common. The most common industrial use of tubular reactors is in systems where a solid catalyst is required. The catalyst is installed in beds or inside tubes in the shell of the reactor vessel, and the process reacting fluid (gas or liquid) flows through the fixed catalyst. 

Plug flow is normally achieved by using a reactor with a large length-to-diameter ratio. Two types of tubular systems behavior need to be distin-... 

The principal use of tubular reactors for kinetic studies is as catalytic fixed-bed reactors in heterogeneous catalysis. They are rarely used for quantitative studies of homogeneous reactions because these are difficult to confine sharply to reactors of this type (see farther below). 

The Hrst type of generic model for shell-and-tube membrane reactors refers to a nonisothermal packed-bed catalytic membrane tubular reactor (PBCMTR) whose cross-sectional view is shown in Figure lO.l. Mathematical models for this type of membrane reactor have been reviewed quite extensively by Tsotsis et al. [1993b]. 

The aim of the preceding discussion on commercial reactors is to give a more detailed picture of each of the major types of industrial reactors batch, semibatch, CSTR, tubular, fixed-bed (packed-bed), and iiuidized-bed. Many variations aird modifications of these commercial reactors are in current use for further elaboration, refer to the detailed discussion of industrial reactors given by Walas. ... 

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