Separation System Design

They are generally calculated for two reasons First, activity coefficients in the very dilute range are experimentally difficult to measure but are commonly needed when designing separation systems, and estimation of infinite-dilution activity coefficients is needed for meaningful extrapolation of whatever experimental data are available. Second, these coefficients are useful when estimating the parameters that are required in several mathematical models used for determining activity coefficients. 

ProMega Corp., Probe-Design Separation System, Technical Manual, 1991. 

The synthesis of the correct structure and the optimization of parameters in the design of the reaction and separation systems are often the single most important tasks of process design. Usually there are many options, and it is impossible to fully evaluate them unless a complete design is furnished for the outer layers of the onion. For example, it is not possible to assess which is better. 

Figure 1.5 A different reactor design leads not only to a different separation system but also to additional possibilities for heat integration. (From Smith and Linnhoff, Trans. IChemE, ChERD, 66 195, 1988 reproduced by permission of the Institution of Chemical Engineers.)...

Despite these problems, a choice of separation system must be made and the design progressed further before it can be properly assessed. 

Once the process route has been chosen, it may be possible to synthesize flowsheets that do not require large inventories of materials in the process. The design of the reaction and separation system is particularly important in this respect, but heat transfer, storage, and pressure relief systems are also important. 

The synthesis of reaction-separation systems. The recycling of material is an essential feature of most chemical processes. The use of excess reactants, diluents, or heat carriers in the reactor design has a significant effect on the flowsheet recycle structure. Sometimes... 

The separation train of the plant is designed to recover important constituents present in the furnace effluent. The modem olefin plant must be designed to accommodate various feedstocks, ie, it usually is designed for feedstock flexibiUty in both the pyrolysis furnaces and the separation system (52). For example, a plant may crack feedstocks ranging from ethane to naphtha or naphtha to gas oils. 

Different MSAs may lead to completely different separation systems designs. The systematic generation procedure given in the separations synthesis algorithm is demonstrated for two potential solvents, hexane and methylene chloride. 

By attempting to maintain process conditions at or near their design values, the process controls so attempt to prevent abnormal conditions from developing within the process. Although process controls can be viewed as a protective layer, this is really a by-product and not the primaiy func tion. Where the objective of a function is specifically to reduce risk, the implementation is normally not within the process controls. Instead, the implementation is within a separate system specifically provided to reduce risk. This system is generally referred to as the safety interlock system. 

Independence. Independence is achieved in the design of systems through functional isolation and physical separation. 

Gopatakrishnan, M., Ramdoss, P., and EI-Halwagi, M. (1996). Integrated design of reaction and separation systems for waste minimization. AIChE Annu. Meet., Chicago. 

Hamad, A. A., Garrison, G. W., Crabtree, E, W., and El-Halwagi, M. M. (1996), Optimal Design of Hybrid Separation Systems for Waste Reduction, Fifth World Congress of Chemical Engineers, Vol. Ill, pp. 453-458, San Diego, California. 

A gaseous emission has a flowrate of 0.02 kmole/s and contains 0.014 mole fraction of vinyl chloride. The supply temperature of the stream is 338 K. It is desired to recover 80% of the vinyl chloride using a combination of pressurization and cooling. Available for service are two refrigerants NH3 and Nj. Thermodynamic and economic data are provided by problem 10.1 and by Dunn etal. (1995), Design a cost-effective energy-induced separation system. 

CHAPTER ELEVEN Design of membrane-separation systems... 

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