Performance of the reactor

The reactor feed may be preheated and the feed pressure may alter. The volumetric flowrate of gases depends on the reactor temperature and pressure at fixed mass flowrate. In many cases, the feed is liquid at room temperature, while the reaction mixture is a gas at the higher temperature in the reactor. In these instances, the performance of the reactor is represented as conversion and selectivity against the liquid hourly space velocity (LHSV). This is defined as... 

The first step is to define the objectives of the flow model, and to identify those flow aspects that are relevant for the performance of the reactor. Then, the engineer must identify and quantify the various times and space scales involved, as well as the geometry of the system. These actions allow the problem to be represented by a mathematical model. Creating this model accurately is the most crucial task in the flow modeling project. 

In the past several years, more attentions have been given to improving mechanical performance of the reactor stripper. Proprietary stripper designs are being offered by the FCC technology licensers in attempts to improve the catalyst/steam contact. 

A high pressure gel permeation chromatograph (GPC) has been used to monitor the performance of the reactor. A novel aspect of the GPC is that, it too, has been put on-line to the process control computer and both data collection and analysis have been made automatic while giving the operator full interactive facilities. 

Thermal study is based on experiments which aim at cooling the process fluid. The process fluid temperature can, for instance, easily vary from 20 to 60 °C. Process fluid can be water at room temperature or heated with thermostat, whereas UF is water at 15 °C. Experiments with water are necessary since they allow the study of thermal performances of the reactor regardless of any other phenomenon (reaction, mass transfer, etc.). As a consequence, thermal study is an important preliminary step before performing chemical reactions. For each experiment, the operating protocol is as follows ... 

Enhanced thermal stability enlarges the areas of application of protein films. In particular it might be possible to improve the yield of reactors in biotechnological processes based on enzymatic catalysis, by increasing the temperature of the reaction and using enzymes deposited by the LB technique. Nevertheless, a major technical difficulty is that enzyme films must be deposited on suitable supports, such as small spheres, in order to increase the number of enzyme molecules involved in the process, thus providing a better performance of the reactor. An increased surface-to-volume ratio in the case of spheres will increase the number of enzyme molecules in a fixed reactor volume. Moreover, since the major part of known enzymatic reactions is carried out in liquid phase, protein molecules must be attached chemically to the sphere surface in order to prevent their detachment during operation. 

CO concentration at the outlet of each zone was continuously measured using a CO analyzer (Shimadzu CGT-7000). To evaluate the performance of the reactors, the conversion of CO for the PBR (Xco) with 4g of catalyst and the time-average conversion of CO for the SCMBR (Tea) with 2g of catalyst in each zone were calculated and compared. It should be noted that the CO concentration wave used for Eq. (1) was obtained whrai the system is at cyclic steady state (after 30 min of operation). 

The important message here is that the overall performance of the reactor may be improved by using an assembly of catalysts that varies though the reactor bed. To what extent such approaches will become viable depends on the cost of varying the catalysts and the savings realized by reducing the size of the high-pressure reactor. 

Study the effect of varying Pe on the performance of the reactor, and compare the resulting performance with perfect plug flow. 

To evaluate the performance of the reactor system, the catalytic hydrogenation of citral to citronellal and citronellol in ethanol was nsed as a sample reaction. The reaction scheme is displayed below. 

Absorbance detectors are also commonly used in combination with postcolumn reactors. Here, most issues of detector linearity and detection limit have to do with optimization of the performance of the reactor. In a typical application, organophosphorus compounds with weak optical absorbances have been separated, photolyzed to orthophosphate, and reacted with molybdic acid, with measurement being performed by optical absorbance.58... 

For biochemical reactions, the performance of the reactor will normally be dictated by laboratory results, because of the difficulty of predicting such reactions theoretically6. There are likely to be constraints on the reactor performance dictated by the biochemical processes. For example, in the manufacture of ethanol using microorganisms, as the concentration of ethanol rises, the microorganisms multiply more slowly until at a concentration of around 12% it becomes toxic to the microorganisms. 

When choosing between different types of reactors, both continuous and batch reactors were considered from the point of view of the performance of the reactor (continuous plug-flow and ideal batch being equivalent in terms of residence time). If a batch reactor is chosen, it will often lead to a choice of separator for the reactor effluent that also operates in batch mode, although this is not always the case as intermediate storage can be used to overcome the variations with time. Batch separations will be dealt with in Chapter 14. 

In this case, the performance of the reactor is governed entirely by single-particle kinetics (e.g., as given in Table 9.1). 

To describe the performance of the reactor, we first assume the particles are all of the same size, and then allow for a distribution of sizes. 

More recent tests have shown that much of the cracking takes place in the transfer line in which the regenerated catalyst is conveyed into the reactor in the stream of oil vapour. The chemical reaction involved is very fast, and the performance of the reactor is not sensitive to the hydrodynamic conditions. 

The feedstock to the TCC reactor varies in its coke-forming properties. This is an important source of disturbance in the kiln operation. Figure 23 shows the effect of a 20% change in coke. The temperature above the air inlet responds with a damped oscillation of the temperature before reaching a steady state 40°F (22°C) above the previous steady state. The temperature at the bottom of the lower zone rises monotonically 75°F (42°C) to the new steady-state value. This rise in catalyst temperature will influence the performance of the reactor, since the catalyst is returned to the top of the reactor after some heat losses from cooling coils in the bottom of the kiln and in the air lift and the separator. The change of temperature... 

Hydrogen production from the bacterial fermentation of sugars has been examined in a variety of reactor systems. Hexose concentration has a greater effect on Hj yields than the HRT. Flocculation also was an important factor in the performance of the reactor (Van Ginkel and Logan, 2005). 

In this situation prediction of the performance of the reactor is straightforward and is dependent only on the stoichiometry of the reaction. The kinetics do not enter the picture. Let us illustrate this behavior with the following ideal contacting patterns. 

As sweep gas flow rate is increased, the performance of the reactor improves until the flow rate is about one thousand times the reactant flow rate. The concentration of all species, but most importantly formaldehyde decreases in the shell side of the reactor as this happens. This increases the driving force for permeation of all species. After increasing this flow rate to a certain point further increases in inert gas flow rate do not change the concentration gradient of any species along the reactor because the shell concentrations of all species is... 

Burghardt et al. (1995) studied, among others, the liquid distribution using needle-type distributors in trickle beds and found that the density of the liquid feed points does have an important effect on the value of the liquid holdup, and thus on the performance of the reactor. They concluded that for a density of more than 5000 feeding points per square meter, the liquid holdup was stabilized. 

The effectiveness of a fixed-bed operation depends mainly on its hydraulic performance. Even if the physicochemical phenomena are well understood and their application in practice is simple, the operation will probably fail if the hydraulic behavior of the reactor is not adequate. One must be able to recognize the competitive effects of kinetics and fluid dynamics mixing, dead spaces, and bypasses that can completely alter the performance of the reactor when compared to the ideal presentation (Donati and Paludetto, 1997). The main factor of failure in liquid-phase operations is liquid maldistribution, which could be related to low liquid holdup in downflow operation, or other design problems. These effects could be critical not only in full-scale but also in pilot- or even in laboratory-scale reactors. 

It is evident that the model predictions are veiy close to the experimental values for a high wetting efficiency, while the model predicts higher conversions for lower wetting efficiencies. This is expected as the simple model assumes complete wetting, i.e. better performance of the reactor. 

Estimate the height of the bed to achieve the same performance of the reactor by using the appropriate simplified model, assuming that the liquid phase remains saturated with 02 throughout the reactor length, plug-flow conditions exist, and the external wetting of the catalyst particle is complete. 

The performance of the reactor will then be expressed in terms of the integrated form of this equation ... 

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