Modelling pilot

Engineering approach based on quantification, including pilot plant work and work with or without mathematical models. Pilot plants are generally 10 times larger than the laboratory reactors but are smaller than production-scale plants. In the first step, the volume of the pilot plant reactor is typically about 50 to 500 1 a second step extends this to 500 to 50001. 

Today, there is no reliable knowledge of the relationship available on this subject, and therefore no design equations based on the operating data and physical properties. It is only the accurate knowledge of the efficacy of the various agitator systems and rheology of the individual media based on results from model, pilot-scale, and industrial-scale systems that makes it possible to select the optimum scale-up rules to be applied. If relevant operational experience is not available, an extensive series of tests in vessels of different sizes must be carried out for the duty concerned. 

Part A gives general guidelines for the design of large commercial fluidized bed reactors with respect to the following aspects (1) solids properties and their effect on the quality of fluidization (2) bubble size control through small solid particle size or baffles (3) particle recovery by means of cyclones (4) heat transfer tubes (5) solids circulation systems (6) instrumentation, corrosion and erosion, mathematical models, pilot plants and scale-up techniques. 

Juraidan, M., Al-Shamali, M., Qabazard, H., Kam, E.K.T. 2006. A refined hydroprocessing multicatalyst deactivation and reactor performance models pilot-plant accelerated test applications. Energy Fuels 20 1354—1364. 

In general, the desorptive behavior of contaminated soils and soHds is so variable that the requited thermal treatment conditions are difficult to specify without experimental measurements. Experiments are most easily performed in bench- and pilot-scale faciUties. Full-scale behavior can then be predicted using mathematical models of heat transfer, mass transfer, and chemical kinetics. 

Comparisons of the complete heat-transfer model with pilot-scale rotary kiln data are shown iu Figure 5 (21) for moisture levels ranging from 0 to 20 wt %. The tremendous thermal impact of moisture is clearly visible iu the leveling of temperature profiles at 100°C. 

The abihty of a four-parameter, two-parallel reaction model to correlate pilot-scale rotary kiln, toluene-desorption results (26) is shown in Figure 6. The model assumes that the adsorbed toluene consists of two fractions, T and F, which are tightly and loosely bound, respectively. 

Fig. 6. Pilot-scale kiln results for a fill fraction of 0.08% at 0.5 rpm and an initial toluene loading, on a dry, calcined, montmorillonite clay adsorbent, of 0.25 wt %, at A, 790°C B, 330°C and C, 190°C. The soHd lines are model fits using equation 24. The model simultaneously fits to all of the data (24).

Specific reactor characteristics depend on the particular use of the reactor as a laboratory, pilot plant, or industrial unit. AH reactors have in common selected characteristics of four basic reactor types the weH-stirred batch reactor, the semibatch reactor, the continuous-flow stirred-tank reactor, and the tubular reactor (Fig. 1). A reactor may be represented by or modeled after one or a combination of these. SuitabHity of a model depends on the extent to which the impacts of the reactions, and thermal and transport processes, are predicted for conditions outside of the database used in developing the model (1-4). 

Ways will indeed be found to use newer technologies to lower the cost of producing R D results, including the use of highly sophisticated modeling and simulation to avoid some laboratory, pilot-plant, and appHcations research altogether. 

The theoretical models caimot predict flux rates. Plant-design parameters must be obtained from laboratory testing, pilot-plant data, or in the case of estabhshed apphcations, performance of operating plants. 

One goal of catalyst designers is to constmct bench-scale reactors that allow determination of performance data truly indicative of performance in a full-scale commercial reactor. This has been accompHshed in a number of areas, but in general, larger pilot-scale reactors are preferred because they can be more fully instmmented and can provide better engineering data for ultimate scale-up. In reactor selection thought must be given to parameters such as space velocity, linear velocity, and the number of catalyst bodies per reactor diameter in order to properly model heat- and mass-transfer effects. 

Process Economics. Relative economics of various ceU culture processes depend heavily on the performance of the ceU line in a system and on the cost of raw materials, particularly the medium. Models are usuaUy developed for the various processes using productivity data obtained from smaU-scale experiments (see Pilot AND MiCROPLANTs). Often, for high value products, the process which ensures the shortest time to market may be the process of choice because of other economic criteria. This is especially tme for pharmaceuticals (qv). RehabUity concerns also often outweigh economic considerations in choosing a process for a high value product. 

During process development, a model can be developed as soon as a conceptual flow sheet has been formulated. This model can be updated as more information about the process is obtained. Even at an early stage in the project, the model can be used to assess the preliminary economics of the process and the effect of technological changes on these economics. The model can aid in interpreting pilot-plant data and allows the study of many process alternatives. 

Systems for evaluating electrolytes for metal electrowinning have been developed and are being used commercially in zinc production (96). Computerized mathematical models of zinc electrowinning cells have been developed and vaUdated by comparison with experimental data taken from pilot-plant cells (97). 

Scale- Up of Electrochemical Reactors. The intermediate scale of the pilot plant is frequendy used in the scale-up of an electrochemical reactor or process to full scale. Dimensional analysis (qv) has been used in chemical engineering scale-up to simplify and generalize a multivariant system, and may be appHed to electrochemical systems, but has shown limitations. It is best used in conjunction with mathematical models. Scale-up often involves seeking a few critical parameters. Eor electrochemical cells, these parameters are generally current distribution and cell resistance. The characteristics of electrolytic process scale-up have been described (63—65). 

RGA Example In order to illustrate use of the RGA method, consider the following steady-state version of a transfer function model for a pilot-scale, methanol-water distillation column (Wood and Berry, Terminal Composition Control of a Binaiy Distillation Column, Chem. Eng. Sci, 28, 1707, 1973) Ku = 12.8, K = -18.9, K. i = 6.6, and Koo = —19.4. It follows that A = 2 and... 

Cycles Design methods for cycles rely on mathematical modeling (or empiricism) and often extensive pilot plant experiments. Many cycles can be easily analyzed using the methods described above apphed to the collection of steps. In some cycles, however, especially those operated with short cycle times or in shallow beds, transitions may not be very fully developed, even at a periodic state, and the complexity may be compounded by multiple sorbates. 

In general, it is not necessary to model Z/T ratios between pilot and commercial units. 

Herbst et al. [International J. Mineral Proce.ssing, 22, 273-296 (1988)] describe the software modules in an optimum controller for a grinding circuit. The process model can be an empirical model as some authors have used. A phenomenological model can give more accurate predictions, and can be extrapolated, for example from pilot-to full-scale apphcation, if scale-up rules are known. Normally the model is a variant of the popiilation balance equations given in the previous section. 

Rajamani and Herbst (loc. cit.) compared control of an experimental pilot-mill circuit using feedback and optimal control. Feedback control resulted in oscillatory behavior. Optimal control settled rapidly to the final value, although there was more noise in the results. A more complete model should give even better results. 

Discs range in size from laboratory models 30 cm in diameter up to production units of 10 meters in diameter with throughputs of 100 ton/hr. Figure 20-82 shows throughput capacities for discs of varying diameter tor different applications and formulation feed densities. When scaling up from laboratoiy or pilot tests it is usual to keep the... 

In today s competitive climate, investigators cannot spend much time on the clarification of the kinetics for a new process. At Union Carbide Corporation in the 1970s the study to replace the old and not very efficient butyraldehyde hydrogenation was done in three months. In another three months a kinetic model was developed and simultaneously tested in an existing single tube in a pilot-plant (Cropley et al,1984). Seldom is a completely new process studied for which no similar example exists in the industry. 

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. 

The new law also establishes a clean fuel car pilot program in California, requiring the phase-in of tighter emission limits for 150,000 vehicles in model year 1996 and 300,000 by the model year 1999. These standards can be met with any combination of vehicle technology and cleaner fuels. The standards become even stricter in 2001. Other states can opt in to this program, though only through incentives, not sales or production mandates. 

Catalytic crackings operations have been simulated by mathematical models, with the aid of computers. The computer programs are the end result of a very extensive research effort in pilot and bench scale units. Many sets of calculations are carried out to optimize design of new units, operation of existing plants, choice of feedstocks, and other variables subject to control. A background knowledge of the correlations used in the "black box" helps to make such studies more effective. 

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