Overall Process Design

Consider the process illustrated in Fig. 1.2. The process requires a reactor to transform the FEED into PRODUCT (Fig. 1.2a). Unfortunately, not all the FEED reacts. Also, part of the FEED reacts to form BYPRODUCT instead of the desired PRODUCT. A 

Thus the complexity of chemical process synthesis is twofold. First, can we identify all possible structures Second, can we optimize each structure for a valid comparison When optimizing the structure, there may be many ways in which each individual task can be performed and many ways in which the individual tasks can be interconnected. This means that we must simulate and optimize 

Our attempt to develop a methodology will be helped if we have a clearer picture of the structure of the problem. If the process requires a reactor, this is where the design starts. This is likely to be the only 

Of course, some processes do not require a reactor, e.g., some oil refinery processes. Here, the design starts with the sepauration system and moves outward to the heat exchanger network and utilities. However, the basic hierarchy prevails. 

The hierarchical nature of process design has been represented in different ways by different authors. A hierarchy of decisions and a process design ladder also have been suggested. 

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In this section, we will begin by discussing overall process designs and process alternatives. Most of the designs come from processes patented by EBC, although other players have contributed recently as well. The alterations to processes come from variations in the raw material to be desulfurized, (diesel vs. crude oil), or from point of application perspective (before or after HDS, in oil field vs. in refinery, etc.) or from changes to reaction schemes (complete desulfurization vs. stopping at an intermediate... 

Feed characterization, particularly for nondesalination applications, should be the first and foremost objective in the design of a reverse osmosis plant. This involves the determination of the type and concentration of the main solutes and foulants in the stream, temperature, pH, osmotic pressure, etc. Once the feed has been characterized, a realistic process objective can be defined. In most cases, some level of pretreatment is needed to reduce the number and concentration of foulants present in the feed stream. Pretreatment necessitates the design of processes other than the RO module, thus the overall process design should use the minimum pretreatment necessary to meet the process objective. Once the pretreatment steps have been determined and the final feed stream defined, the RO module can be selected. 

Electrodialysis equipment and process design The performance of electrodialysis in practical applications is not only a function of membrane properties but is also determined by the equipment and overall process design. As far as the stack design is concerned there are two major concepts used on a large scale. One is the sheet-flow concept, which is illustrated in Figure 5.3 and the other is the so-called tortuous path concept, which is illustrated in Figure 5.5. 

The first two effects are calculated directly from the overall process design. The frictional losses are obtained from the compressor power requirements. They amount to a total exergy destruction of 10 MW. Heat exchanger losses due to heat transfer in Units 1-6 (excluding the reformer) can be evaluated from the exergy exchange calculations they amount to 49 MW for a 20K temperature difference. 

Because of the high olefin yields and low light ends make, the MTO process does not require the high cost separation equipment of a conventional ethylene recovery unit. Figure 12.12 shows the overall process design, including product... 

Therefore, we know of about 1850 m of BPM currently (or soon) in operation, mainly for the production of specialty and fine chemicals, such as amino and organic acids. The limited number of EDBM plants in operation is the result of many factors, mainly industry concerns over reliability and cost. The relatively high investment of EDBM systems limits its use so far to higher value products. However, improvement in stack and plant design, as well as overall process design, allows its use for the production of a growing number of products. Already, four new plants have been installed in the last 2 years. 

If AP, is unacceptable, it is necessary to assume a new pass arrangement and repeat the calculations. The heat transfer coefficient of the shell and tube heat exchanger is only acceptable if the design is within limits of the allowable pressure drop for the streams being heated or cooled. The selection of the optimum allowable pressure drop for an exchanger is a function of the overall process design. 

An important example of this kind is a contribution of cracking processes to partial oxidation of propane and higher hydrocarbons. In particular, in the case of catalytic propane ODH, the formation of lower hydrocarbons—first of all ethylene and methane—can substantially reduce propylene selectivity. The analysis of possible homogeneous and heterogeneous pathways of C-C bond breaking can provide valuable guidelines for further improvement of catalyst formulation and/or overall process design. 

J. S. Kussi, H. J. Leimkiiler, R. Peme Overall Process Design and Optimization AIChE Symp. Ser. 96(2000)315-319. 

Use Top-Doum/Bottom-Up Design Strategies Alternately. Approaches that scope out options in light of overall process design olgectives should be used alternately with approaches that evaluate these objectives at the local level for fea lify. 

Many a bonded part has failed in use because the conditions of cleanliness and the attention to surface preparation routinely used in manufacture were greatly different from those used to prepare test specimens. Methods of cleaning and the application of a primer, when one is needed, must be considered as an essential part of the manufacturing process. It is foolish to make qualification tests on any pretreatment that is not entirely compatible with the overall process design. 

In-line premixing of the reactants with a static mixer was selected since this method of operation was compatible with the overall process design, and the mixing intensity required could be expected at the size and throughput required. 

To further explore this question, a parametric study was made by this author to determine the effect of the thermal condition of the feed upon the overall process design of a tow er and the heat quantities involved. This work was based on analyzing three binary hydrocarbon systems so that the calculations could be easily treated by hand. However, the relationships developed also apply to multi-component systems. 

Wrapping up, both cobalt and iron catalysts should be considered as options for the FT reactor in the BTL process. A number of scenarios for the BTL process should be developed with both type of catalysts, while the overall process design should be coupled with catalyst developments in both cases in order to clearly prove the superiority of the one catalyst system over the other for commercial applications. 

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