Type and Number of Unit Operations

Because of the complex composition of most groundwaters, no one unit operation is capable of removing all of the contaminants present. It may be necessary to combine several unit operations into one treatment process to remove effectively the contaminants required. To simplify and make visible the selection of the applicable treatment trains, a number of unit operations and the waste types for which they are effective are presented in Table 8.1. 

The foregoing description of some of the basic experimental work should provide a sufficiently clear idea of the type of experiments involved. In order to prevent this survey from becoming too long, the end results of these studies will be summarized in a more condensed form. The fractionation process will be divided into a number of unit operations, and the experimental results observed will be briefly stated. 

The use of an acid plant to treat roaster and sinter process off-gases was practised at 18 of the surveyed plants, and Figure 3 illustrates the type and number of acid units operated. 

Production of a metal is usually achieved by a sequence of chemical processes represented as a flow sheet. A limited number of unit processes are commonly used in extractive metallurgy. The combination of these steps and the precise conditions of operations vary significantly from metal to metal, and even for the same metal these steps vary with the type of ore or raw material. The technology of extraction processes was developed in an empirical way, and technical innovations often preceded scientific understanding of the processes. 

Duty types. S, S, and. S5 as discussed in Chapter 3 are normally applicable to crane and hoist motors. For duty types S4 and 5. the duty cycle per unit time is greater than S, . The most important factor is the number of switching operations per hour. A temperature rise in the motor occurs during acceleration, braking and reversing. 

Turbine mainlenance. This should be based on equivalent engine time, whieh is the funetion of temperature, type of fuel used, and number of starts. Figure 19-21 shows the eorreetion that ean be applied to running hours for intermittent-duty units with high-start/stop operation. 

All rocket motor costs per unit, and therefore rocket proplnt costs, are most sensitive to the number of units being produced and to the number of different formulations mixed in a given time interval, by the same equipment, so that a direct comparson based only on processes or proplnt types are meaningless. There are also inherent difficulties in comparing NC base proplnts with composite propints. The former are made in government plants (some of which are operated by private industry) for the most part and so accounting for indirect costs (taxes, depreciation, insurance, and return on investment) cannot be compared to the situation... 

Contaminant properties can also affect treatment costs. The type and amount of contaminants will impact the efficiency of any SVE technology. These impacts include the number of extraction wells, the power of the blower unit, and the length of operation required to achieve project goals. Contaminant properties will also impact the type of ancillary technology(ies) selected (D22449H, p. 4-4). 

In some circumstances the magnitudes of the translation vectors must be taken into account. Let us demonstrate this with the example of the trirutile structure. If we triplicate the unit cell of rutile in the c direction, we can occupy the metal atom positions with two kinds of metals in a ratio of 1 2, such as is shown in Fig. 3.10. This structure type is known for several oxides and fluorides, e.g. ZnSb20g. Both the rutile and tlie trirutile structure belong to the same space-group type PAjmnm. Due to the triplicated translation vector in the c direction, the density of the symmetry elements in trirutile is less than in rutile. The total number of symmetry operations (including the translations) is reduced to... 

Rarely in the pharmaceutical industry is a new plant built to accommodate a new process or product It may happen in the petrochemical industry, where economies of scale mean that product-specific plants are designed from scratch and then continuously de-bottlenecked over a number of years to increase and optimize productivity, but it is not the case in the pharmaceutical industry, where the number of types of unit operations in use is generally fairly small and fixed. Within a multi-purpose chemical plant commonly found in the batch chemical industry, it is common practice for process designers to make do with what is available on a given site to avoid capital expenditure and plant shut-down for modifications. 

From a green engineering perspective, the number and types of unit operations can also be counted ... 

Bubble-cap assemblies in the form of round bell caps are commonly used with diameters ranging from 4 to 7 in. A 6-in.-diameter cap with a 4-in.-diameter riser is a standard size used in many industrial operations. Cap diameters as large as 8 in. have been employed successfully in some operations, and 3-in. caps with 2-in. risers are used in many vacuum towers. Tunnel caps are ordinarily 3 to 6 in. wide and 12 or more in. long. Comparison of the two types shows that tunnel caps have the advantage of a smaller number of units for installation for a given slot and riser area, but the round caps are more... 

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