Small-scale equipment

Minimum Fluidizing Velocity U,nj, the minimum fluidizing velocity, is frequently used in fluid-bed calculations and in quantifying one of the particle properties. This parameter is best measured in small-scale equipment at ambient conditions. The correlation by Wen audYu [A.l.Ch.E.j., 610-612 (1966)] given below can then be used to back calculate d. This gives a particle size that takes into account effects of size distribution and sphericity. The correlation can then be used to estimate U, at process conditions, if U,nj cannot be determined experimentally, use the expression below directly. 

The scale-up ratio is defined as the relationship between productivities of large-scale and small-scale equipment items, i.e. 

However, for small scale equipment, Cheng (1993) and Xu (1993) measured the circulation times of a single tagged particle in a 150 mm diameter fluidized bed coater with a draft tube and found that typical circulation times were between 2-10 seconds. Robinson and Waldie (1978) made similar measurements in a 6" diameter conventional spouted bed and found mean circulation times in the range of 3-6 seconds. 

This secondary effect of materials is illustrated by the difficulties encountered, in a recent study [54], when attempts were made to correlate CO concentrations measured in small scale and full scale fire tests. The same small scale equipment (typically the cone calorimeter rate of heat release test) could predict adequately a number of very important full scale fire properties, including ignitability, rate of heat release, amount of heat release and smoke obscuration. It could not, however, be used to... 

Small scale equipment used for reactor process development in the biochemical field, such as small scale fermentation reactors and closed loop reactors, have their merits for general reactor development. These reactors may be as large as 20 liters in volume, and are well equipped and instrumented. They are not reviewed, however, in this book. 

For small vessels and slow reactions, corrections must be made because of the heat content of the reaction vessel itself. For large-scale reaction vessels and for rapid reactions, the system will be close to adiabatic operations. This aspect must be taken into account in scale-up. In effect, the extrapolation of data obtained in small-scale equipment has limitations as discussed in [193]. In case of a runaway, the maximum temperature in the reaction system is obtained from the adiabatic temperature rise, that is, Tmax = (Tr + ATad). In reality, the adiabatic temperature rise is significantly underestimated if other exothermic reaction mechanisms occur between Tr and (Tr + ATad). Therefore, a determination must be made to see if other exothermic events, which may introduce additional hazards during a runaway, occur in the higher temperature range. This can determine if a "safe operating envelope" exists. 

The lower and upper explosive limits (LEL and UEL) of gases (really gas-air mixtures) are determined in small-scale equipment by spark ignition at ambient temperature and pressure. The flammability range established by this method may deviate from the actual range at the commercial scale. At elevated temperatures, the flammability range is expected to increase. A similar phenomenon occurs at higher pressures, while at lower pressures, ignition may become impossible. 

Minimum Fluidizing Velocity LO, the minimum fluidizing velocity, is frequently used in fluid-bed calculations and in quantifying one ol the particle properties. This parameter is best measured in small-scale equipment at ambient conditions. The correlation by Wen... 

There are several methods to achieve appropriate scale-up of mixing. The first method involves geometric similarity. This technique employs proportional scale-up of geometric parameters of the vessel. The scaled-up parameters may include such geometric ratios as T)/r ratio, where D is diameter of the impeller and T is diameter of the tank, and Z/T ratio, where Z is the height of the liquid in the vessel. Similar ratios are compared for both the small-scale equipment DiTi) and the larger size equipment (D2T2). For example,... 

The basis of the scale-of-agitation approach is a geometric scale-up with the power law exponent, = 1 (Table 1). This provides for equal fluid velocities in both large- and small-scale equipment. Furthermore, several dimensionless groups are used to relate the fluid properties to the physical properties of the equipment being considered. In particular, bulk-fluid velocity comparisons are made around the largest blade in the system. This method is best suited for turbulent flow agitation in which tanks are assumed to be vertical cylinders. 

Table 1 Common Values Assigned to the Power Law Exponent, n. When Comparing Large- to Small-Scale Equipment...

The equipment used to perfonn the compaction operation is a tablet press. The small-scale equipment from which one might scale up would include ... 

In some areas, suppliers make available small scale equipment that can be used to explore suitable ranges of operating conditions, or they may do the work themselves with benefit of their extensive experience. One engineer in the extrusion pelleting field claims that merely feeling the stuff between his fingers enables him to properly specify equipment because of his experience of 25 years with extrusion. 

The major problem in scale-up (Hussain, 2002 Leuenberger, 2002b) is that the formulation is optimized on a small-scale equipment, but is for obvious reasons no longer optimal for a large-scale equipment. A possible solution is the introduction of a semicontinuous process using a... 

Experimental measurements yielded only a fivefold extension of the reaction cycle time, a difference largely caused by heat storage effects in the small-scale equipment used, which disproportionately enhanced the cooling effect observed in the inert bed control experiment. Despite this less satisfactory result, the desorptive cooling concept would still seem to offer potential for dramatic improvement in performance for regenerative heat exchange processes. 

Then, a survey of micro reactors for heterogeneous catalyst screening introduces the technological methods used for screening. The description of microstructured reactors will be supplemented by other, conventional small-scale equipment such as mini-batch and fixed-bed reactors and small monoliths. For each of these reactors, exemplary applications will be given in order to demonstrate the properties of small-scale operation. Among a number of examples, methane oxidation as a sample reaction will be considered in detail. In a detailed case study, some intrinsic theoretical aspects of micro devices are discussed with respect to reactor design and experimental evaluation under the transient mode of reactor operation. It will be shown that, as soon as fluid dynamic information is added to the pure experimental data, more complex aspects of catalysis are derivable from overall conversion data, such as the intrinsic reaction kinetics. 

In 1979, because of a lack of large samples, boiler fuel test programs will be limited to small scale equipment. However, in 1980, large samples of liquids in the 5,000-10,000 barrel range should become availabel from the H-Coal pilot plant at Catlettsburg, Kentucky and the Exxon Donor Solvent process at Baytown, Texas. It would be preferable to run a number of tests utilizing different utility sites and types of electric generation... 

It was further assumed that mixer and settler holdup times were the same as used in our small scale equipment. Mass transfer between the phases in the mixer was further assumed to be instantaneous to facilitate the calculations. In some cases this may lead to underestimation of solvent dose, but in other cases to overestimation. It is believed that these errors largely cancel out over the whole process. It was further assumed that a small common buffer tank was used for the purified recirculated solvents, thus giving an averaging effect on the solvent doses in the first and third cycles. 

Double-ring connections are commonly used on most small scale equipments, when the service pressure is below 400 bar. These connections are perfectly safe and reliable when the screwing procedures are strictly followed. Otherwise, the rings are not strongly attached to the tubing and a brutal rupture may occur on pressurization. 

In general, small scale models have too much pumping capacity and too little impeller zone shear rate to be typical of the performance to be expected in a full scale prototype. Thus, it is normally necessary to purposely scale down the pumping capacity, and increase the shear rate on small scale equipment to more closely duplicate the performance which will be expected on full size units. 

TIjffective use of the vast coal reserves of the United States requires quantitative information on their conversion behavior in commercially important reactions. Studies using small-scale equipment and aimed at determining the effects of temperature, pressure, particle size, and heating rate on the rapid thermal decomposition of coal in atmospheres of both helium (pyrolysis) and hydrogen (hydropyrolysis) have been in... 

The evaluation of pressurized wood-slurry liquefaction by the LBL process of wood-water slurries was performed mainly in small-scale equipment (Ergun, 1981 Davis, 1983). Oils similar to those produced by the PERC process were obtained, but at lower yields. In the late 1970s and early 1980s, the PERC process was evaluated in a PDU (Thigpen and Berry, 1982). The purpose of... 

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