Tubular flow reactors configurations

Figure 11.3 Tubular flow reactor-some possible configurations (a) low LID (b) high LID (c) tubular arrangement...

After a few preliminary runs using a caking eastern bituminous coal and several reactor configurations, it was found that better results could be obtained with a non-caking coal in an entrained down-flow tubular reactor. The coal was dropped down into a tubular reactor through which hydrogen was passed down-flow and entrained and carried the coal down through the heated tube. 

Other variables of importance in designing these tubular pyrolysis reactors include the mass velocity (or flow velocity) of the gaseous reaction mixture in the tubes, pressure, steam-to-hydrocarbon-feedstock ratio, heat flux through the tube wall, and tube configuration and spacing. Pressure drop in the reactor is of major importance, especially because of the extremely high flow velocities normally employed. 

Tubular reactors are also used to carry out some multiphase reactions. Wamecke et al. (1999) reported use of a computational flow model to simulate an industrial tubular reactor carrying out a gas-liquid reaction (propylene oxide manufacturing process). In this process, liquid is a dispersed phase and gas is a continuous phase. The two-fluid model discussed earlier may be used to carry out simulations of gas-liquid flow through a tubular reactor. Warnecke et al. (1999) applied such a model to evaluate the influence of bends etc. on flow distribution and reactor performance. The model may be used to evolve better reactor configurations. In many tubular reactors, static mixers are employed to enhance mixing and other transport processes. Computational flow models can also make significant contributions to understanding the role of static mixers and for their optimization. Visser et al. (1999) reported CFD... 

The tubular reactor is a vessel through which the flow is continuous. There are several configurations of tubular reactors suitable for multiphase work, e.g. for liquid-solid and gas-liquid-solid compositions. The flow patterns in these systems are complex. A fixed bed reactor is packed with catalyst, typically formed into pellets of some shape, and if the feed is single phase, a simple tubular plug-flow reactor may suffice (Figure 1.1). Mixed component feeds can be handled in modifications to this. 

A systematic approach to the design of a reactor should start by discussing the field of velocity distributions. Much progress has been achieved in this area and the hydrodynamic characterization of a great variety of reactors is already known. For the sake of brevity, we will concentrate on two types of systems a perfectly mixed reaction space and a fully developed unidirectional flow in a tubular reactor. In practical terms this is not a serious limitation in computational fluid mechanics, commercially available calculating codes can be used to solve almost any other form of reactor configuration. 

The tubular reactor is so named because the physical configuration of the reactor is normally such that the reaction takes place within a tube or length of pipe. The idealized model of this type of reactor is based on the assumption that an entering fluid element moves through the reactor as a differentially thin plug of material that fills the reactor cross section completely. Thus, the terms piston flow or plug flow reactor (PFR) are often employed to describe the idealized model. The contents of a specific differential plug are presumed to be uniform in temperature and composition. This model may be used to treat both the case where the tube is packed with a solid catalyst (see Section 12.1) and the case where the fluid phase alone is present. 

Figure 19.10 A matrix of membrane reactor configurations (al) semibatch tank reactor with ESU (SBR or BR-ESU) (a2 and a3) batch reactor with flat and tubular ISU (BR-ISU) (hi and b2) continuously stirred reactor with flat and tubular ISU (CSTR-ISU) (c) plug-flow reactor with ESU (PFR-ESU) and (d) PER with ISU (PFR-ISU).

Two alternative reactor configurations were then investigated in the laboratory (1) agitated thin-film reactor and (2) tubular reactor with static mixers. The reaction time was found to be at most a few tenths of a second and yield increased with increasing agitator speed in the thin-film reactor and increasing flow rate in the tubular reactor. Semicommercial scale reactors of both types were assembled and tested. 

Reactor configurations involved in continuous emulsion polymerization include stirred tank reactors, tubular reactors, pulsed packed reactors, Couett-Taylor vortex flow reactors, and a variety of combinations of these reactors. Some important operational techniques developed for continuous emulsion polymerization are the prereactor concept, start-up strategy, split feed method, and so on. The fundamental principles behind the continuous emulsion polymerizations carried out in the basic stirred tank reactor and tubular reactor, which serve as the building blocks for the reaction systems of commercial importance, are the major focus of this chapter. 

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