Plug flow operation

Cyclohexane. The LPO of cyclohexane [110-82-7] suppUes much of the raw materials needed for nylon-6 and nylon-6,6 production. Cyclohexanol (A) and cyclohexanone (K) maybe produced selectively by using alow conversion process with multiple stages (228—232). The reasons for low conversion and multiple stages (an approach to plug-flow operation) are apparent from Eigure 2. Several catalysts have been reported. The selectivity to A as well as the overall process efficiency can be improved by using boric acid (2,232,233). K/A mixtures are usually oxidized by nitric acid in a second step to adipic acid (233) (see Cyclohexanol and cyclohexanone). 

In advance, comparative fixed-bed measurements were undertaken. It was ensured that the performance of a plug-flow operation with both flows having the same direction is superior to trickle-bed operation, using counter-flow instead. The plug flow was assumed to model the slug-flow behavior in the micro reactor. 

In any real situation, reactants only flow through the reactor because there is a difference in pressure between the inlet and the outlet. Methods for calculating the pressure drop in pipes and packed beds have been outlined in Chap. 1. Often, the pressure drop is negligible compared with the total pressure and it is usual to assume that a tubular reactor with plug flow operates at constant pressure. 

For an ideal plug-flow operation, the material balance (3.286) is greatly simplified ... 

All of these roasting furnace reactors operate continuously. They are noncatalytic gas-solid heterogeneous reactors. The multiple hearth has characteristics similar to plug flow operation. The flash roaster approaches CSTR, and the third option is a fluidized bed configuration. 

Table II. Steps for Ensuring Plug Flow Operation in Laboratory Reactors...

On an industrial scale, the ampoule process is duplicated by a continuous plug flow operation, where the raw material enters at one end and exits at the other end of the reactor. During the residence time in such a reactor, there is absolutely no removal of the furfural generated, as in the ampoules. 

In addition to intensity and UV demand of the water, the exposure time also affects the energy dosage that the target organisms absorb. Exposure time is controlled by the residence time of the water in the reactor. Continually maintaining the required residence time is not always possible, but the system design should maximize plug-flow operation. 

Fluidized bed crystallizers operated in particulate mode (usually the case with hquids) can also come very close to plug flow operation. An example of such crystallizers will be shown in Example 7-6. 

Many of the modern combustion processes can be characterized by relatively low reaction rates compared to the modern catalytic processes operated in chemical reactors [67]. Therefore, these combustion processes do require lower gas velocities and higher solids circulation rates. On the other hand, many catalytic gas-phase reactions, including FCC, Fischer-Tropsch synthesis and oxidation of butane, utilize a relatively high gas velocity in the riser to promote plug flow operating conditions and short contact times between the gas and solids. 

Another model, which will not be analyzed, is the plug-flow reactor with recycle shown in Fig. 6-1. The reactor itself behaves as an ideal tubular type, but mixing is introduced by the recycle stream. When the recycle rate becomes very large, ideal stirred-tank performance is obtained, and when the recycle is zero, plug-flow operation, results. The response data on the actual reactor are used to evaluate the recycle rate and then the conversion is estimated for a plug-flow reactor with this recycle rate. 

For adiabatic plug-flow operation, FITN = 0, and the energy balance equation is... 

The one-pass, plug flow operation of a thin-film evaporator is an advantage for minimizing thermal degradation of a heat sensitive product in an evaporation step. The mean residence time in the evaporator can be just seconds, rather than minutes or hours in a recirculating evaporation system. For this reason, thin-film evaporators are widely used for heat sensitive food, pharmaceutical, and other chemical products. Also, it should be noted that the thin-film evaporator can be operated at a higher temperature to make a better separation, whereas care must usually be taken to keep the product temperature lower in an evaporation system with longer residence times (see Fig. 21, later in this chapter). 

If the reaction intermediates are potentially hazardous, their concentration levels should be kept minimal in the reactors. For continuous processes, consider a plug-flow operation instead of a... 

These limits give the minimum velocities necessary for plug flow operation. Operation at lower Reynolds numbers can be expected to result in a radial profile of velocities in the reactor, with the result that the time of transit of increments of reactant varies along the radius of the reactor cross section. This in turn means that a sample of effluent from the reactor contains increments with different transit times whose average transit time is the nominal space time for that run. 

Continuous plug flow operation for long processes, which most bioprocesses are. 

Plug flow operation - very narrow residence time distribution ... 

The residence time distribution of the gas may deviate from plug-flow operation by dispersion and bypassing effects. (We will learn in the Section 4.10.3 why plug-flow operation is mostly advantageous compared to mixed flow.)... 

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