Scaled laboratory models

Small, properly scaled laboratory models operated at ambient conditions have been shown to accurately simulate the dynamics of large hot bubbling and circulating beds operating at atmospheric and elevated pressures. These models should shed light on the overall operating characteristics and the influence of hydrodynamics factors such as bubble distribution and trajectories. A series of different sized scale models can be used to simulate changes in bed behavior with bed size. 

The scale-up of filtration centrifuges is usually done on an area basis, based on small-scale tests. Buchner funnel-type tests are not of much value here because the driving force for filtration is not only due to the static head but also due to the centrifugal forces on the Hquid in the cake. A test procedure has been described with a specially designed filter beaker to measure the intrinsic permeabiHty of the cake (7). The best test is, of course, with a small-scale model, using the actual suspension. Many manufacturers offer small laboratory models for such tests. The scale-up is most reHable if the basket diameter does not increase by a factor of more than 2.5 from the small scale. 

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... 

Example 2-3 Scale-Up of Pipe Flow. We would like to know the total pressure driving force (AP) required to pump oil (/z = 30 cP, p = 0.85 g/cm3) through a horizontal pipeline with a diameter (D) of 48 in. and a length (L) of 700 mi, at a flow rate (Q) of 1 million barrels per day. The pipe is to be of commercial steel, which has an equivalent roughness (e) of 0.0018 in. To get this information, we want to design a laboratory experiment in which the laboratory model (m) and the full-scale field pipeline (f) are operating under dynamically similar conditions so that measurements of AP in the model can be scaled up directly to find AP in the field. The necessary conditions for dynamic similarity for this system are... 

These results indicate that our scaled-up model ecosystems are more useful for studying system processes than processes that function in individual components of the environment. In this regard, a preliminary large scale ecosystem study could be very useful to indicate parameter limits such as overall degradation rates and likely concentrations of parent compounds plus metabolites over time. Such information would be useful in the design of metabolic studies in various components of the ecosystem. In addition, the large scale ecosystem study could also be used to determine if processes derived under laboratory conditions continue to function and/or predominate when combined in a complex system. 

As the next step in multiphasic hydrogenation, the design and implementation of a continuously driven loop reactor as a laboratory-scale plant model led to comparable selectivity applying the same water soluble ruthenium-based catalyst system. 

Example 5.4 Design a geometrically similar laboratory-scale cold model fluidized bed to simulate the hydrodynamics of a large-scale fluidized bed combustor. Also specify the operating conditions for the cold model. The combustor is a square cross section column with a width of 1.0 m and a height of 6 m. The fluidized bed combustor is operated at a temperature of 1,150 K, a superficial gas velocity of 1.01 m/s, and a bed height of 1.06 m. Particles with a density of2,630 kg/m3 and a diameter of677ptm are used for the combustor. The cold model is operated at a temperature of 300 K. Air is used for both the cold model and hot model fluidized beds. The physical properties of air are... 

Many methods have been used to size relief systems area/volume scaling, mathematical modeling using reaction parameters and flow theory, and empirical methods by the Factory Insurance Association (FIA). The Design Institute for Emergency Relief Systems (DIERS) of the AIChE has performed studies of sizing reactors undergoing runaway reactions. Intricate laboratory instruments as described earlier have resulted in better vent sizes. 

A problem arises, e.g., when model (laboratory, bench-scale) measurements are to be performed in a so-called cold model , but the industrial plant operates at high temperatures (petrochemicals T = 800 - 1000 °C). How can we ascertain that the laboratory model system behaves hydrodynamically similarly to that in the industrial plant Here, different temperature dependence of physical properties (viscosity, density) may cause problems. 

Operating scale (laboratory vs. industrial) affects the behavior of chemical reaction systems. It is critical that we develop hydrodynamic models for those systems that are scale sensitive. This will require a collaboration between academic and industrial groups to collect data necessary for commercial-scale equipment. Once the hydrodynamic models have been developed and validated, kinetic models can be integrated with them. 

Integrated Testing. Although the individual steps of the process have been demonstrated in laboratory experiments, testing of the entire system is necessary in order to proceed along the path to commercialization. The integrated testing is currently planned to be comprised of three sequential steps, i.e., the laboratory model, the process development unit (PDU), and the "pilot-scale" unit. 

Suzuki, T., Hirouse, R., Takemura, M., Morita, A., Yano, K., and Hyvarinen, K. Comparison ol NO, Emission Between Laboratory Modelling and Full Scale Pyroflow Boilers, in Circulating Fluidized Bed Technology III" (Basu, P., Horio, M., and Hasatani, M., eds.), pp. 387-392. Pergamon Press, Oxford (1991). 

Several questions are raised by the overall problem of manufacturing chemicals with multifunctional properties how can the operations be scaled-up from the laboratory model to an actual plant Will the same product be obtained and its properties preserved What is the role of equipment design in determining the properties of the products These questions are strongly sustained by the fact that the existing scaling-up procedures cannot show how such end-use properties such as colour, flowability, sinterability, biocompatibility and many others can be controlled. 

The laboratory scale physical model of the catalytic sulfur dioxide oxidation is a 0.05 m-diameter reactor containing 3 mm-diameter pellets of catalyst over a height of 0.15 m. The bed is flushed through at 430 °C by a gas flow that contains 0.07 kmol S02/kmol total gas, 0.11 kmol 02/kmol total gas and 0.82 kmol N2/kmol total gas. The gas spatial velocity is 0.01 m/s. 

With respect to the evolution of the phenomenon considered in Table 6.7, if 3g, a , and a are the scaling factors (the coefficients that multiply the laboratory model parameters in order to obtain the value of the prototype s parameters) then these can be written as ... 

It is important to note that a good agreement in the validation tests described above does not unequivocally indicate that the scaling up is correct, especially when the dimensions of the scales between the different LMs are significantly different from those required by the basic laboratory model. However, if the agreement between the various models is not good, it is impossible to use the same model design to predict the behaviour of the basic laboratory model. 

The operating variables to be considered include temperature, pressure, time, modifier affects, and agitation of the vessel. These variables are typically determined by the physical properties of the cleaning solvent and solute, e.g., solubility of the solute in the solvent, mass transfer rates of the solute into the bulk solvent, and reactivity of the solvent with the solute. These properties are determined in the laboratory from a scaled working model of the process or found in a source reference book. 

For systematic study of several gas-liquid chemical reactions using a laboratory model bubble-cap column, Sharmaet al. (S23) have shown that the presence of electrolytes, size of caps, type of slots, ionic strength, liquid viscosity, and presence of solids do not affect the mass-transfer rates. These rates chiefly depend on the gas and liquid flow rates (S23, M2). The influence of the superficial gas flow rate on ki, and Icq is indicated in Fig. 20. Interfacial area a" per unit area of plate (or per unit floor area) for plate diameters varying between 0.15 and 1.20 m have been grouped in Fig. 21, which with the following correlations (S23) can be used to scale up bubble-cap plates up to 2 or 3 m in diameter ... 

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