Process-Related Design Considerations

A wide variety of protective coating types and systems is available for corrosion control on external and internal surfaces of structural and process plant in marine and offshore engineering. These are discussed in detail elsewhere in this text, and the purpose here is to highlight the critical importance of certain design and related operational aspects which affect both the selection and performance of protective coating systems. The following design considerations should be made ... 

In absolute terms, the quantities of reactor solids found in various processes do vary considerably. The rate of accumulation is related to several factors, such as coal characteristics, recycle solvent quality and reactor design. However, it can be stated in general terms that liquefaction of low rank coals (sub-bituminous C and lignites) does result in higher rates of accumulation of solids than do similar operations with bituminous coals. For example, during normal operations of the SRC-I pilot plant at Wilsonville, Ala., it has been found that the amount of solids retained varies from about 0.2-0.5 wt.% (moisture-free) for bituminous coals to 1.0-1.9 wt.% (moisture free) for a subbituminous C coal (Wyodak) (72). Exxon also reports much larger accumulations for lignites and subbituminous coals than those found for bituminous coals (73). 

The primary design consideration at any oil, gas or related facility should be the protection of employees and the general public from the effects of an explosion or fire. In all cases highly populated occupancies should be located as far as practical upwind of the process or storage areas. Where this cannot be practically... 

Industrial solutions invariably contain dissolved impurities that can increase or decrease the solubility of the prime solute considerably, and it is important that the solubility data used to design crystallisation processes relate to the actual system used. Impurities can also have profound effects on other characteristics, such as nucleation and growth. 

The continuous development of the modem process industries has made it increasingly important to have information about the properties of materials, including many new chemical substances whose physical properties have never been measured experimentally. This is especially true of polymeric substances. The design of manufacturing and processing equipment requires considerable knowledge of the processed materials and related compounds. Also for the application and final use of these materials this knowledge is essential. 

Formulation of the volume-related liquid-side mass transfer coefficient k a leaves the questions open, of whether this quantity should be regarded and investigated as such, or as the product of two parameters fet and a independent of one another. Whereas for industrial problems and design criteria only k a is important, for an in depth consideration of the process it is certainly interesting to establish, how the two components of this quantity depend upon the material and process-related parameters, since a deeper insight into this relationship can also provide hints for a directed optimization of the absorption process. 

Tab. 7.1 shows the established applications in the field of membrane gas separation. One of the new and currently small appHcations shown in Tab. 7.1 is natural gas dehydration. Problems related to this separation wiU be discussed in the last part of this chapter (basic process design considerations). 

In reactive distillation, chemical reactions are assumed to occur mainly in the liquid phase. Hence the liquid holdup on the trays, or the residence time, is an important design factor for these processes. Other column design considerations, such as number of trays or feed and product tray locations, can be of particular importance in reactive distillation columns. Moreover, because chemical reactions can be exothermic or endothermic, intercoolers or heaters may be required to maintain optimum stage temperatures. Column models of reactive distillation must include chemical reaction equilibrium or kinetic equations along with the material and energy balance equations and the phase equilibrium relations. These models and methods for solving them are discussed in Chapter 13. 

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