Rigorous Design Methods

Often for preliminary calculation, the ideal conditions are assumed, followed by more rigorous design methods. The first approximation ideal basis calculations may be completely satisfactory, particularly when the activities of the individual components are 1.0 or nearly so. 

The rigorous design method is based on generally accepted closed-form models. The adhesive behaviour in the models is assumed to be linearly elastic. Only the formulae used in the calculation of the temporary maximum joint resistance require the complete shear stress—shear strain curve or the elastic—plastic model of the adhesive to be known. As adhesives typically have a non-linear shear behaviour, using only the linear part of the stress—strain curve brings added conservatism to the models with respect to the actual joint resistance. 

The development of rigorous design methods for LPG treaters has been hampered by the lack of liquid-liquid equilibrium (LLE) data for amines and sour hydrocarbon liquids. Early designs were based on empirical rules of thumb and field experience with existing units operating under similar conditions. 

There is a tendency for both axial and radial dispersion of mass to occur when a fluid flows through a packed bed. Since the bed diameter is normally far greater than the particle diameter in an adsorption bed, it is common not to have to consider the effects of radial dispersion. Hence the prevalence of plug and axially dispersed plug flow models in rigorous design methods. 

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