Klaus Lucas

Pareto optimization of a combined cycle power system as a decision support tool for trading off investment vs. operating costs

The monetary optimization of thermodynamic processes may be approached by inherently thermodynamic frameworks like exergo-economic analysis, or a rigid direct cost evaluation is applied. This paper, treating the optimization of a combined cycle power plant, follows the second path. Operation and investment costs are usually treated as a combined value by means of an annualization factor. Due to the rather far-stretching time horizon of turbine energy conversion systems, differing behaviour of those contributions with time, and varying subjective weighting and assumptions of future developments, this conventional subsumption is not necessarily a sensible one to identify the best solution for a given decision situation. It is therefore favorable to address both costing goals independently and identify the pareto set of the problem prior to a final decision on which parametrization of the system should be chosen. A numerical pareto optimization technique based on an evolutionary base strategy is discussed that addresses this type of problem in an efficient and easy to adapt manner.

Applied statistical thermodynamics

This text guides the reader from the foundations of statistical thermodynamics including the theory of intermolecular forces to modern computer-aided applications in chemical engineering and physical chemistry. The foundations of quantum and statistical mechanics are presented in a simple way, and their applications to the prediction of fluid phase behaviour of real systems are demonstrated. A particular effort is made to introduce the reader to explicit formulations of intermolecular interaction models and to show how these models influence the properties of fluid systems. The established methods of statistical mechanics - computer simulation, perturbation theory, and numerical integration - are discussed in a style appropriate for newcomers and are extensively applied. Worked examples illustrate how practical calculations should be carried out.

Conformal solutions: which model for which application?

Abstract Shukla, K.P., Luckas, M., Marquardt, H. and Lucas, K., 1986. Conformal solutions: which model for which application? Fluid phase Equilibria, 26: 129–147. Various forms of conformal solution theories are discussed and compared to computer simulations for Lennard-Jones mixtures under rather different conditions. It is found that the simple VDW1-theory is applicable when the ratio of the energy parameters is 1.5, and the ratio of the size parameters is 1.1. The same region of applicability is found for the Mean Density Approximation (MDA). Two models using explicitly known properties of the hard-sphere mixture, i.e., the Hard-Sphere Expansion theory (HSE) and a particular version of the Hard-Sphere Perturbation theory (WCA-LL-GH), have also been tested. The HSE is not complete unless a consistent method is found to calculate the hard-sphere diameter. The overall best results are found for WCA-LL-GH. While WCA-LL-GH turns out to be limited in applicability to size ratios smaller than 1.3 and appears to be inaccurate for particular cases, it is definitely the best model available today.

On the thermodynamics of cogeneration

Cogeneration of various energy forms in a single piece of equipment has the potential of saving primary energy in comparison to separate generation. The amount of energy saving depends on the thermodynamic parameters of the systems to be compared and can be presented in a closed formula. For the particular case of cogeneration in a steam turbine a thorough thermodynamic analysis on the basis of exergy losses reveals the reasons for the higher efficiency. It is due to the facts that on producing the useful heat Q a transfer of this heat over the temperature difference between the heat intake of the cycle and the temperature of the heat demand is replaced by a power cycle and that separate power production is avoided altogether. This leads to a rational allocation of primary energy and in turn of emissions to the coupled energy forms.

Experimental vapor-liquid equilibria in the systems R 22-R 23, R 22-Co2, Cs2-R 22, R 23-Co2, Cs2-R 23 and their correlation by equations of state

Abstract Roth H., Peters-Gerth P. and Lucas K., 1992. Experimental vapor-liquid equilibria in the systems R 22-R 23, R 22-CO2, CS2-R 22, R 23-CO2, CS2-R 23 and their correlation by equations of state. Fluid Phase Equilibria, 73: 147-166. Vapor-liquid equilibria in systems with polar molecules tend to show a rather complex phase behavior. In order to investigate the phase boundaries in mixtures of dipolar and quadrupolar components five binary systems of the components R 22, R 23, CO2 and CS2 have been selected. Experimental VLE data for the systems R 22-R 23, R 22-CO2, CS2-R 22, R 23-CO2 and CS2-R 23 are reported in this paper at temperatures between 254 and 473 K and pressures up to 25 MPa. The data were correlated with one empirical and one semi-empirical equation of state.

Economic optimization of non-sharp separation sequences by means of evolutionary algorithms

Abstract The general distillation sequence synthesis problem featuring the separation of multicomponent feed streams into multicomponent products is addressed. Potential flowsheets include stream bypassing and mixing and use sharp separations as well as non-sharp splits where key component distribution is allowed. Compared to conventional sharp distillation sequence synthesis, this leads to a mixed-integer non-linear programming problem of increased complexity, including non-convexities as well as multi-modalities. Product specifications create additional constraints while simultaneously call for a rigorous modeling of the non-key distribution. A synthesis method is proposed that models the various flowsheet configurations with a new and flexible superstructure concept and connects the gradient-free optimization technique of application-orientedly developed Evolutionary Algorithms (EAs) to the rigorous modeling capabilities of the Aspen Plus ™ simulation system, thus enabling realistic process design and cost objective function calculation. The re-examination of two published examples illustrates the applicability and the potential of the approach.

Absorption of sulfur dioxide in dilute aqueous solutions of sulfuric and hydrochloric acid

Abstract Spectrophotometric measurements of combined phase and chemical equilibrium have been performed for SO 2 + H 2 SO 4 + H 2 O and SO 2 + HCl + H 2 O systems at 298 K and atmospheric pressure. The vapour and liquid phases have been analysed in situ using a fibre optic based technique described in an earlier publication. The measurements have been performed up to an equilibrium partial pressure of about 1 kPa for sulfur dioxide. The concentration range of the acids have been varied up to 0.5 M for H 2 SO 4 and 1.0 M for HCl. A thermodynamic model is presented which allows the interpolation and the extrapolation of the experimental results. The calculated partial pressures of SO 2 in the SO 2 + H 2 SO 4 + H 2 O system are compared with existing literature values. The experimental results for the SO 2 + HCl + H 2 O system show an anomaly in the uv-spectrum of molecular dissolved sulfur dioxide. The absorption band for SO 2 is shifted towards higher wavelength. This effect is interpreted in terms of the formation of a weak complex SO 2 Cl − .

Molecular models for fluids

Nomenclature 1. Introduction 2. Foundations 3. The ideal gas 4. Excess function models 5. Equation of state models Appendices Index.

Heat Integration of Batch Processes

Heat integration is the synthesis of heat exchanger networks by connecting process streams requiring cooling and heating. Primary energy is saved by utilizing the heat of a hot stream to warm up a cold stream instead of using fossil fuels. For stationary processes pinch analysis has been established to find the optimum heat integration. An appropriate, though not optimal method for heat integration in batch processes is OMNIUM. In this paper, it is demonstrated that the conventional OMNIUM method can be improved systematically in order to achieve a higher heat recovery.

Thermodynamics of the xenon+methyl chloride system

Abstract The total vapour pressure of the xenon + methyl chloride system has been measured as a function of composition at 175.44 and 182.32 K. The resulting data have been used to evaluate the excess Gibbs functions GE at the same temperatures. The excess enthalpy and excess molar volume have also been measured at 182.32 K. The system shows large positive deviations from Raoults law but negative volumes on mixing. These results are compared with theoretical predictions of a recent molecular theory and of standard engineering methods. The calculations show the superiority of the molecular theory over more empirical procedures such as those based on the Redlich-Kwong equation of state or the regular-solution model.