Egon Eckert

New approach to the characterisation of petroleum mixtures used in the modelling of separation processes

Characterisation of complex mixtures is a common tool especially in oil processing industry. Characterisation procedures result in experimentally gained characterisation curves, but for the simulation of industrial processes the definition of a substitute mixture is required. Traditionally, a system of pseudocomponents is derived from the True Boiling Point (TBP) characterisation curve, but there are a number of disadvantages, e.g. the physical properties of pseudocomponents must be estimated by unreliable empirical methods. The new approach to the characterisation of complex mixtures is based on representing the original mixture by a system of real components. Such substitute mixture is fully defined, it has a chemical character, and physical properties can be simply retrieved from databases. Utilisation of a substitute mixture of real components in the simulation of crude oil processing proved that the new approach could replace the traditional one in normal boiling temperature ranges where real components are available. Both approaches could be also easily combined.

CATALYTIC OXIDATION OF CO ON CuO/Al2O3.I. REACTION RATE MODEL DISCRIMINATION

Abstract Carbon monoxide oxidation by pure oxygen on a porous catalyst of the type CuO on Al2O3 is studied in a laboratory differential recycle reactor. Reaction rate data obtained under atmospheric pressure and within the temperature range 135-165°C are used for reaction rate model evaluation. For a preliminary screening of models the method of quasi-linearized regression is proposed and successfully used. Box-Hills procedure is applied for discrimination between the remaining small group of reaction rate models.

Calculation of multicomponent distillation of non-ideal mixtures by a short-cut method

Abstract The Smith-Brinkley method has been modified for use in computing non-ideal multicomponent distillations. The procedure proposed is of particular advantage for rapid calculating hydrocarbon fractionators.

Modelling of dynamics for multiple liquid—vapour equilibrium stage

Abstract A rigorous dynamic model for multiple liquid—vapour equilibrium stages has been developed. A global approach to the calculation of the non-adiabatic multiple liquid—vapour equilibrium flash has been used for this purpose. The structure of the system of model equations is adaptively changed in the course of integration. The response of the stage to a change in process parameters (heat duty, feed composition) is illustrated for mixtures of the type vapour—liquid—liquid and vapour—liquid—liquid—liquid.

Improvements in the selection of real components forming a substitute mixture for petroleum fractions

Complex mixtures, particularly petroleum fractions, usually need to be suitably modeled before providing the simulation and other types of chemical engineering calculations. The most convenient way is to describe the original mixture by a substitute mixture. The formerly published approach based on the employment of substitute mixtures of real components can be improved in order to get a closer match between the behavior of the original and substitute mixtures. In the first phase of the algorithm, a new concept of a band around the characterization curves brings wider possibilities for the selection of real components into the substitute mixture. The second phase, which is used to determine the composition of the substitute mixture, can be also improved by considering the global or bulk properties of the original mixture if available. Typically, some of the properties e.g. liquid density, molecular mass and PNA (Paraffinic/Naphthenic/Aromatic carbon) analysis can be measured and used to improve the adjustment of the composition. The improved algorithm is illustrated by an example.

Mathematical modelling of selected characterisation procedures for oil fractions

Models of two important characterisation procedures for oil and oil fractions, ASTM D86 (ASTM = American Society for Testing of Materials) and EFV (Equilibrium Flash Vaporization), were presented. The purpose was to provide a basis for the construction of substitute mixtures of real components used in modelling and simulation of chemical engineering processes instead of original complex mixtures. It was shown how to deal with a possible problem of higher index of differential-algebraic model of the ASTM D86. A number of examples proved the adequacy of the presented models.

Simulation of stage separation columns based on the block short-cut approach

Abstract A generalization of the short-cut approach for the modelling and design of stage separation columns has been developed. The block short-cut method can be used for complex columns and non-standard problem specifications. The column is partitioned into several separation sections (blocks), each modelled by a universal short-cut model. The overall simulation model is solved by the global Newton-Raphson method. Very low memory and CPU time requirements enable the block short-cut approach to be utilized for fast simulation and control of columns in industrial practice.

Global approach to the computation of separations by approximate methods

Abstract A global approach to the computation of simple separation columns for non-ideal mixtures by approximate methods is described. The procedure based on a modification of the Smith—Brinkley method enables us to compute practically any type of problem formulation, i.e. both simulation and design problems. The technique can also be used for formulation of semirigorous procedures for general arrangements of more complex types of equipment.