The Hierarchy

Choice of reactor. The first and usually most important decisions to be made are those for the reactor type and its operating conditions. In choosing the reactor, the overriding consideration is usually raw materials efficiency (bearing in mind materials of construction, safety, etc.). Raw materials costs are usually the most important costs in the whole process. Also, any inefficiency in raw materials use is likely to create waste streams that become an environmental problem. 

The design of the reactor usually interacts strongly with the rest of the flowsheet. Hence, a return must be made to the reactor design when the process design has progressed further. 

Choice of separator. For a heterogeneous mixture, separation usually can be achieved by phase separation. Such phase separation normally should be carried out before any homogeneous separation. Phase separation tends to be easier and usually should be done first. 

Distillation is by far the most commonly used method for the separation of homogeneous fluid mixtures. No attempt should be made to optimize pressure, reflux ratio or feed condition of distillation in the early stages of design. The optimal values will almost certainly change later once heat integration with the overall process is considered. 

The most common alternative to distillation for the separation of low-molecular-weight materials is absorption. Liquid flowrate, temperature and pressure are important variables to be set, but no attempt should be made to carry out any optimization at this stage. Other commonly used separation methods are adsorption and membranes. 

Maslow referred to the first three levels as lower order needs. The upper two levels he called the ego needs. The first of the upper needs is esteem—having self-respect and the respect and recognition from others. The highest level need is self-fulfillment or self-actualization—thinking and feeling that one has fully realized one s potential. This is the upper end of the success and significance staircase discussed in Chapter 2. 

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All too often safety and health (and environmental) considerations are left to the final stages of the design. Returning to the hierarchy of design illustrated by the onion diagram in Fig. 1.6, such considerations would add another layer in the diagram outside the utilities layer. This approach leaves much to be desired. 

The hierarchy of models is complemented by a variety of methods and tecluiiques. Mesoscopic models tliat incorporate some fluid-like packing (e.g., spring-bead models for polymer solutions) are investigated by Monte Carlo... 

Walking through the Hierarchy of Chemical Structure Representation... 

Standard reference materials provide a necessary but insufficient means for achieving accuracy and measurement compatibiUty on a national or international scale. Good test methods, good laboratory practices, well-qualified personnel, and proper intralaboratory and intedaboratory quaUty assurance procedures ate equally important. A systems approach to measurement compatibiUty is ikustrated in Figure 2. The function of each level is to transfer accuracy to the level below and to help provide traceabiUty to the level above. Thus traversing the hierarchy from bottom to top increases accuracy at the expense of measurement efficiency. 

Fig. 3. The hierarchy of protein stmctures (a) primary stmcture (see Table 1 for amino acid code) (b) secondary stmcture (c) tertiary stmcture and (d)...

As discussed in the introduction, the hierarchy set forth by the USEPA in the Pollution Prevention Act establishes an order to which waste-management activities should be employed to reduce the quantity of waste generated. The preferred method is source reduction, as indicated in Fig. 25-1. This approach actually precedes traditional waste management by addressing the source of the problem prior to its occurrence. 

The treatment of waste is the third element of the hierarchy and should be utilized only in the absence of feasible source reduction or recychng opportunities. Waste treatment involves the use of chemical, biological, or physical processes to reduce or eliminate waste material. The incineration of wastes is included in this categoiy and is considered preferable to other treatment methods (i.e., chemical, biological, and physical) because incineration can permanently destroy the hazardous components in waste materials (Ref. 4). It can also be employed to reduce the volume of waste to be treated. 

It would obviously be desirable to eliminate the generation of waste. Practical alternatives are to minimize it by reduction at source or to recycle it. Table 16.7 illustrates the hierarchy of waste minimization practices. Source reduction includes increased process efficiency economies in the use of energy are also relevant, e.g. it may result in a decrease in the consumption of fossil fuels ... 

Table 16.7 Waste minimization in the hierarchy of waste management practices...

Initially, a system s hierarchy is identified for subsystems, sub-subsystems and so on to the components for which data must be found. The top event specifies system failure subsystems required for operation of the system in the mode specified are input to the top event s OR gate. Redundancy is represented by the redundant systems inputting an AND gate. This process of grouping subsystems under OR gates, if they can individually fail a function, or under AND gates if concurrent failures are necessary, is continued to the component or support system level until the tree is completed. This process grades the hierarchy from top to bottom, down the fault tree. 

Determine the hierarchy of documentation which you intend to produce to define your quality system (the number and content of the volumes of procedures etc.)... 

The hard-sphere excess chemical potential p that appears on the left-hand side of the hierarchy is related to the compressibility factor Z = pV/pkT,... 

The equilibrium theory of homogeneous fluids may be constructed by using the hierarchy of the direct correlation functions [48]. This approach has been of much utility for the development of the theory of inhomogeneous simple fluids. The hierarchy of the direct correlation functions is defined by the following relation... 

To describe an arbitrary nonequilibrium evolution of the adsorbate we need the whole hierarchy, or at least a suitably truncated subset. We can close the hierarchy at the level of 2-site correlators by a factorization of higher correlators with 1-site overlap [58,59]... 

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