System and operating variables

The influence of a number of the system variables relating to powder and liquid properties, etc., has already been discussed in Section 1 above. With proper control of these variables and of the pan operating conditions, it is possible within limits to influence agglomerate properties such as shape, size and porosity. A discussion of such factors has been given by Pietsch [24] and by Ball [25]. 

A guide to disc dimensions (diameter, depth), speed of rotation, throughput and power input is given in Section 2.1.3 below for normal or average operating conditions. For a specific powder/binder feed material, however, optimization of disc conditions requires trials with the actual machine. Only a qualitative guide to expected effects of some variables can be given here. 

Agglomerate size is controlled primarily by retention time on the disc and the amount of added binder liquid. The relationship between these variables is shown qualitatively in Fig. 3.11. Residence time and hence pellet size can 

To obtain a consistent product, inclined discs must be operated uniformly not only mechanically but also with regard to solids and liquid binder properties and feed rates. 

Available models range from laboratory units 1 ft (0.3 m) diameter to production models greater than 20 ft (6.1 m) diameter. Pietsch [24] has surveyed scale-up for inclined disc agglomerators and offers the following relationships for the approximate design of a unit of diameter, D, in metres  

---

System and operating variables factors affecting product size... 

Two studies have been concerned with measurement of the interfacial area obtained by agitation of liquid-liquid systems. Each of these investigations relied on the use of a photoelectric probe which measured the light transmission of the two-phase dispersion. Vermeulen and co-workers (V2) made measurements in two geometrically similar, baffled vessels of 10- and 20-in. diameter. They used a very simple four-blade paddle-like stirrer, with a tank-to-impeller diameter ratio of about 1.5, and a 0.25 blade-width/impeller-diameter ratio. The impeller was located midway between the top and bottom of the vessel, which had a cover and was run full. Impeller speeds varied from about 100 to 400 r.p.m. A wide variety of liquids was employed. Volume fractions of dispersed phase varied from 10% to 40%. The mean droplet diameters observed ranged from 0.003 to 0.1 cm. The results were correlated with a mean deviation of about 20% by an empirical equation relating the specific interfacial area near the impeller to several system and operating variables as follows ... 

The existence of secondary processes brings about another limitation of gel chromatography it is often rather difficult and sometimes even impossible to compare directly the data obtained with different chromatographic systems or under different operational variables. The same limitation is valid for the transfer of experimental results from one type of sample to another — even if an identical column system and operational variables are applied. It is advisable to check the possible influence of secondary processes when separating an unknown sample. 

Los Alamos National Laboratory performed separate statistical analyses using the Failure Rate Analysis Code (FRAC) on IPRDS failure data for pumps and valves. The major purpose of the study was to determine which environmental, system, and operating factors adequately explain the variability in the failure data. The results of the pump study are documented in NUREG/CR-3650. The valve study findings are presented in NUREG/CR-4217. 

Another approach to the design problem is to determine empirical correlations based on experimental work and to adopt these correlations for scale-up. In many of the published works the latter approach is investigated. The correlations are such that the volumetric mass-transfer coefficient is generally reported as a function of one or more of the equipment, system, or operating variables cited above. Empirical correlations can be used confidently for scale-up only for equipment that has complete geometrical similarity to the... 

The selectivity for various rotational speeds should be determined with stirrers of small and large Ds/D,-, while maintaining the other design and operating variables constant (see Table 5.4-26). Plots of yields of unwanted products S versus N, x99, and PA r should then be made for both stirrers to determine the independent parameter which best correlates the data for both stirrer systems. 

These factors can be broadly classified as equipment variables, system variables, and operating variables. 

Definition of variables relevant to the process state variables, such as cells, substrates, and product concentrations, that characterize the system studied and operational variables, that represent particular conditions of the system, that may be initial or fixed conditions such as initial concentrations, feeding rates, etc. ... 

Besides some environmental and operational variables, the state variables of systems must be known, namely the amounts of active biocatalyst, of starting materials, of products, byproducts and metabolites. 

This nucleation/emulsifier utilization phenomena is one reason why batch kinetics and product characteristics are difficult to extrapolate from batch reactor to continuous stined-tank systems. A comparison of Equations (8.4) and (8.10) illustrates this in a quantitative manner for Smith-Ewart Case 2 kinetics. It should be noted that both formulation and operational variables (such as ) can influence nucleation and polymerization rates differently in the two reactor systems — even for the same kinetic model. One can change some aspects of this potential disadvantage of a CSTR by use of a small particle size seed in the feed stream or by placing a continuous tubular reactor upstream of the CSTR. These techniques can remove the nucleation phenomena tom the CSTR system which can then be used exclusively to grow the seed particles. 

The physical and chemical behavior of the system requires the definition of key design decision variables. For one-stage and multistage levels those decision parameters and operational variables include operational pressure and temperature, chemical reaction kinetics i.e. equilibrium or rate-limited chemical reaction), mass/heat transfer regime, phase velocity, residence time of the reactive phase and temporal operation i.e. batch, fed batch and continuous). 

This presentation has focused on corrosion test methods in open recirculated cooling tower systems. This area is the most challenging, difficult, and important area of corrosion testing in industrial water. For economic and environmental reasons, water and inhibitor lost through blowdown must be minimized. Cooling tower systems are the systems that are most subject to operational upsets and operational variables. 

In order to better understand the system behavior, several theoretical models have been developed describing the process. Different mechanisms are considered, and assumptions are made in order to predict the performance of the pressure swing adsorption cycle. These theoretical studies also allow gain an insight into the effect of the cycle steps and operating variables. 

---