Large-scale reactors

All the mentioned precautions do not make the operating mode of these tubular reactors close to that of large-scale reactors. The outside observer... 

The predictions checked in the pilot-plant reactor were reasonable. Later, when the production unit was improved and operators learned how to control the large-scale reactor, performance prediction was also very good. The highest recognition came from production personnel, who believed more in the model than in their instruments. When production performance did not agree with model predictions, they started to check their instruments, rather than questioning the model. 

Figure 8.2 Dimensions of the 4.3 i and 121 large-scale reactors after Zaimer and Jones,...

Operation of a large-scale reactor with thousands of parallel channels is expected in 2011. 

Scahng up will probably continue to be a problem since large reactors carmot be as efficient as small laboratory reactors. However, it may be possible to make laboratory or pilot-plant reactors that are more similar to large-scale reactors, allowing more rebable validation of the simulations and process optimization. The time from laboratory-scale to full-scale production should be shortened from years to months. 

The large scale reactor simulations represent a step towards realistic... 

Figure 1.23 Large-scale reactor with microstructured internals tested at the industrial site of Degussa and developed jointly by a project team of several partners [137],...

Conversion/selectivity/yield - benchmarking to large-scale reactors... 

Large-scale reactors have low quantum yields as radiation does not penetrate deeply into the reaction vessel [72, 74]. As a consequence, high-power lamps have to be used causing a lot of excess heat and even posing safety constraints. These energy sources produce locally high quantities of radicals which may not mix thoroughly with the rest of the solution. Therefore, they may not find a second reaction partner, but instead react by themselves. This radical combination reduces selectivity and creates additional heat. 

The desired product is P, while S is an unwanted by-product. The reaction is carried out in a solution for which the physical properties are independent of temperature and composition. Both reactions are of first-order kinetics with the parameters given in Table 5.3-2 the specific heat of the reaction mixture, c, is 4 kJ kg K , and the density, p, is 1000 kg m . The initial concentration of /I is cao = 1 mol litre and the initial temperature is To = 295 K. The coolant temperature is 345 K for the first period of 1 h, and then it is decreased to 295 K for the subsequent period of 0.5 h. Figs. 5.3-13 and 5.3-14 show temperature and conversion curves for the 63 and 6,300 litres batch reactors, which are typical sizes of pilot and full-scale plants. The overall heat-transfer coefficient was assumed to be 500 W m K. The two reactors behaved very different. The yield of P in a large-scale reactor is significantly lower than that in a pilot scale 1.2 mol % and 38.5 mol %, respectively. Because conversions were commensurate in both reactors, the selectivity of the process in the large reactor was also much lower. 

The deposition rate is not uniform over the grounded electrode. A common requirement for large-scale reactors is a 5% difference in deposition rate over a certain electrode area, preferably the complete electrode. Using this, the 2D model would predict a useful electrode area of about. 0%, i.e., an electrode radius of about 4 cm. 

FIG. 23. The partial pressure of silane (Pa) for a large-scale reactor with (a) ring inlet and (b) show-erhead inlet. Note the difference in axial and radial scales. Discharge settings are a total pressure of 20 Pa, a power of 5 W. and an RF frequency of 50 MHz. (From G. J. Nienhuis, Ph.D. Thesis. Universiteit Utrecht, Utrecht, the Netherlands, 1998, with permission.)... 

Prediction of cavitational activity distribution based on theoretical analysis of the bubble dynamics equations can be used to identify the regions with maximum pressure fields in a large scale reactor and then may be small reactors can... 

At times the net rates of chemical/physical processing achieved using ultrasonic irradiations are not sufficient so as to prompt towards industrial scale operation of sonochemical reactors. This is even more important due to the possibility of uneven distribution of the cavitational activity in the large scale reactors as discussed... 

It has been shown that the results obtained are applicable to large scale reactors and to blends of coals. 

On the basis of different assumptions about the nature of the fluid and solid flow within each phase and between phases as well as about the extent of mixing within each phase, it is possible to develop many different mathematical models of the two phase type. Pyle (119), Rowe (120), and Grace (121) have critically reviewed models of these types. Treatment of these models is clearly beyond the scope of this text. In many cases insufficient data exist to provide critical tests of model validity. This situation is especially true of large scale reactors that are the systems of greatest interest from industry s point of view. The student should understand, however, that there is an ongoing effort to develop mathematical models of fluidized bed reactors that will be useful for design purposes. Our current... 

In practice, large-scale reactors operate close to adiabatic conditions on loss of cooling which causes maximum increases in temperature. In smaller reactors, the temperature increase depends on the heating of coolant and reactor, and the heat loss to the reactor frame and confined coolant as well. 

Step 3—size vent for large scale reactor. 

Heraeus markets a multicathode metal depletion system. In the system, one or two anodes face a large number of permeable cathodes, e.g. in form of copper strips similar to expanded metal. [90,234a], Plattner and Comninellis have developed large scale reactors total plate electrode surface ca. 20 m2, cf. ref. [140]. 

Annable, D., Application of the Temkin kinetic equation to ammonia synthesis in large-scale reactors, Chem. Eng. Sci. 1(4), 145-153 (1952). 

The many factors outlined above which affect reaction rates suggest that considerable caution is advisable when utilising laboratory data for the design of large-scale reactors. It is essential first to locate the reaction volume or volumes. This, in the case of the absorption of CO2 into aqueous ammonia liquid discussed above, the fast reaction between dissolved CO2 and dissolved ammonia occurs in a small volume of liquid close to the gas—liquid interface. The forward reaction rate is, therefore, proportional to the gas—liquid interfacial area. The conversion of the initially fomed NH2COONH4 to (NH4)2COa by hydrolysis is a much slower reaction and takes place throughout the whole volume of the liquid phase. Similarity would therefore dictate that the interfacial area per unit liquid volume should be the same in experimental and full-scale reactors. 

The development of microfabrication technologies for ceramic and metallic materials has significantly promoted, during the last decade, research in the field of microreactors, characterized by higher specific productivity, better control of operating conditions and a higher standard of intrinsic safety than large-scale reactors [33, 34]. 

Fluidized catalytic cracking reactors, called cat crackers or FCC reactors, are one of society s most important large-scale reactors. On an average, each such... 

In some cases, direct scale-up may be impracticable, for example because of blockage of the small-scale relief line. The requirement for complete emptying of the small-scale reactor by two-phase relief may also not be met in practice. If this occurs for a tempered system, the problem could be overcome by using a small-scale relief system from the bottom of the test reactor to simulate one at the top of the large-scale reactor. This procedure would not be safe for untempered reactions. 

Choosing a laboratory reactor for the purpose of investigating a particular reaction is rather like choosing a reactor for an industrial scale operation, in that the choice depends mainly on the intrinsic speed of the reaction—/as/, moderately fast, or slow. As with large scale reactors, the value of P- lk2CBLDA /kL is a useful... 

According to the data for volumetric mass transfer coefficient measured in the device on a small pilot plant scale, for a certain load of flue gas to be processed, the required total volume of the reactor under consideration would be very small, only about 1/3 that of existing wet FGD equipment. In addition, the arrangement of the internal wet cyclone shown in Fig. 7.23 enables the reactor to have simultaneously high ash-removal efficiency. The reactor is especially suitable for the wet desulfurization of flue gas with hydrated lime or dilute ammonia solution as the absorbent. The design of the large-scale reactor suitable for a power station has now been accomplished and is expected to be applied industrially in the very near future. 

The use of continuous immobilized cell biofilm reactors eliminates downtime and hence results in superior reactor productivity (2,3). Adsorbed cell continuous biofilm reactors have been shown to favorably affect process economics (4). Application of these reactors reduces capital and operational cost, thus making the process simpler. Within these reactors, cells are immobilized by adsorption, which is a simpler technique than other techniques such as entrapment and covalent bonding (5). Adsorption is a simple technique and can be performed inside the reactors without the use of chemicals, whereas entrapment and covalent bonding are complicated techniques and require chemicals for bond formation. In anaerobic systems, such as butanol production, adsorption can be performed anaerobically within the reactor. An additional advantage of adsorption is that cells form uniform biofilm layers around the support, which lessens diffusion resistance compared to entrapped and covalently bonded cells. Hence, these reactors are called biofilm reactors. Because of reduction in diffusion resistance, the reaction rate is enhanced. For this reason, adsorption was chosen as the technique to be employed for Clostridium beijerinckii BA101 cell immobilization to produce butanol. In addition to being simple, it has the potential to be used in large-scale reactors. In the present study, clay brick was chosen as the cell adsorption support. It is available at a low cost and is easy to dispose of after use. 

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