Equipment Operation Variables

Equipment used for (a) low- and (b) medium-pressure agglomeration (a.l) screen extruder, (a.2) basket extruder, (a.3) cylindrical-die screw extruder, (b.l) flat-die extruder, (b.2) cylindrical-die extruder, (b.3) intermeshing-gears extruder. 

Equipment used for high-pressure agglomeration (a) compacting roller press, (b) briquetting roller press. 

Appropriate liquid content, expressed as fraction X, for an optimum agglomeration process, can be represented by the following relation  

In terms of optimum rotation speed of tumbling agglomeration units, normally rotating drums, this can be calculated by 

For rotating discs used in agglomeration purposes, the power P and the mass flow rate Q can be calculated by the following equations  

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The spray flux captures the impact of equipment operating variables on nucleation, and as such is very useful for scale-up if nucleation rates and nuclei sizes are to be maintained constant. The overall impact of dimensionless spray flux on nucleation and agglomerate formation is illustrated in Fig. 21-106, with agglomerates increasing with increased spray flux as clearly governed by Eq. (21-106) for the case of rapid drop penetration. 

Another basic consideration is whether crystallization is best carried out on a batch basis or on a continuous basis. The present tendency in most processing plants is to use continuous equipment whenever possible. Continuous equipment permits adjusting of the operating variables to a relatively fine degree in order to achieve the best results in terms of energy usage and product characteristics. It allows the use of a smaller labor force and results in a continuous util-... 

The use of appropriate instruments to monitor equipment operation and relevant process variables will detect, and provide warning of, undesirable excursions. Otherwise tliese can result in equipment failure or escape of chemicals, e.g. due to atmospheric venting, leakage or spillage. Instruments may facilitate automatic control, emergency action such as coolant or pressure relief or emergency shutdown, or the operation of water deluge systems. 

Generally, a eonstant value of a partieular operating/equipment variable is used. Some examples of seale-up based on eonstant operating variables as frequently used in fermentation are shown in Table 11-4. The properties, whieh ean be kept eonstant at the different seales, are ... 

Ejectors do not respond to wide fluctuations in operating variables. Therefore, control of these systems must necessarily be through narrow ranges as contrasted to the usual control of most other equipment. 

Most FCC problems are due to changes in the feedstock, catalyst, operating variables, and/or mechanical equipment. As previously stated. 

Even though equipment operations have understandable but controllable variables that influence processing, the usual most uncontrollable variable in the process can be the plastic material. The degree of properly compounding or blending by the plastic manufacturer, converter, or in-house by the fabricator is important. Most additives, fillers, and/or reinforcements when not properly compounded will significantly influence processability and fabricated product performances. 

These variables are controllable within limits to produce useful products. What is important to appreciate is that during the past many decades improvements in equipment have made exceptional strides in significantly reducing operating variabilities or limitations (Fig. 8-78). This action will continue... 

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... 

LES with some model of the SGS flow and transport phenomena, suited for reproducing—at the level of the grid cell size—rather detailed transient fields of velocities and other transport variables in full-scale process equipment operated under turbulent-flow conditions. 

Operating variables for plant equipment that are subject to constraints. 

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

Normal safety precautions for laboratory work and for the use of electrical equipment, especially variable temperature accessories, must be observed. The thermal analysis experiment involves high temperatures and there is a danger of being burned. Consult instrument operating manual for specific cautions regarding operation. 

The main variables in the operation of atomizers are feed pressure, orifice diameter, flow rate and motive pressure for nozzles and geometry and rotation speed of wheels. Enough is known about these factors to enable prediction of size distribution and throw of droplets in specific equipment. Effects of some atomizer characteristics and other operating variables on spray dryer performance are summarized in Table 9.18. A detailed survey of theory, design and performance of atomizers is made by Masters (1976), but the conclusion is that experience and pilot plant work still are essential guides to selection of atomizers. A clear choice between nozzles and spray wheels is rarely possible and may be arbitrary. Milk dryers in the United States, for example, are equipped with nozzles, but those in Europe usually with spray wheels. Pneumatic nozzles may be favored for polymeric solutions, although data for PVC emulsions in Table 9.16(a) show that spray wheels and pressure nozzles also are used. Both pressure nozzles and spray wheels are shown to be in use for several of the applications of Table 9.16(a). 

The nature and sizing of equipment depends on the economic values and proportions of the phases as well as certain physical properties that influence relative movements of liquids and particles. Pressure often is the main operating variable so its effect on physical properties should be known. Table 11.1 is a broad classification of mechanical processes of solid-liquid separation. Clarification is the removal of small contents of worthless solids from a valuable liquid. Filtration is applied to the recovery of valuable solids from slurries. Expression is the removal of relatively small contents of liquids from compressible sludges by mechanical means. 

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