Georg Fieg

A hybrid genetic algorithm for synthesis of heat exchanger networks

A new hybrid genetic algorithm for optimal design of heat exchanger networks is developed. The mathematical model used in the algorithm is based on an explicit solution of stream temperatures of heat exchanger networks with the stage-wise superstructure. By taking heat transfer areas and heat capacity flow rates as genes in the genetic algorithm, the thermal performance and total cost of arbitrary heat exchanger networks can be calculated explicitly and therefore the individuals (heat exchanger networks) can always be feasible. This characteristic makes the algorithm suitable for large scale synthesis problems. The genetic algorithm is combined with simulated annealing algorithm, local optimizing strategy, structure control strategy and other strategies so that the structural search ability of the algorithm is conspicuously enhanced. The examples presented in this work revealed special search abilities in both structure space and continuous variable space.

An evolutionary approach for multi-objective dynamic optimization applied to middle vessel batch distillation

In this paper, a new approach is presented to perform multi-objective dynamic optimizations of novel batch distillation utilizing an evolutionary algorithm. The contribution is divided into two major parts. First, the development of an efficient hybrid evolutionary algorithm covering multi-objective mixed integer dynamic optimization problems is presented. The efficiency of the optimization solver is proven by several complex test problems. Second, the application of the algorithm is shown by the optimization of a middle vessel batch distillation. The challenging non-linear dynamic model, which takes the start-up phase into account, is solved in Aspen Custom Modeler. It could be proven that the proposed evolutionary algorithm can be applied to complex mathematical problems. Likewise the algorithm was found to successfully handle the optimization of middle a vessel batch distillation. The results show the feasibility of the proposed methodology and a significant increase in profitability of the process.

Approach for the Determination of Heat Transfer Coefficients for Filling Processes of Pressure Vessels With Compressed Gaseous Media

For fast and effective simulation of filling processes of pressure vessels with compressed gaseous media, the governing equations are derived from a mass balance equation for the gas and from energy balance equations for the gas and the wall of the vessel. The gas is considered as a perfectly mixed phase and two heat transfer coefficients are introduced. The first one is the mean heat transfer coefficient between the gas and the inner surface of the pressure vessel, and the second one is the heat transfer coefficient between outer surface of the vessel and the surroundings. Because of the heat capacity of the wall of the pressure vessel, heat transfer from the compressed gas to the vessel wall strongly influences the temperature field of the gas. Until now no correlations have been available for the heat transfer coefficient between inflowing gas and inner surface of the vessel. To solve this problem, a computational fluid dynamics tool is used to determine the gas velocities at the vicinity of the inner surface of the vessel for a number of discrete surface elements. The results of a large amount of numerical experiments show that there exists a unique relationship between the gas velocity at the inlet and the tangential fluid velocities at the vicinity of the inner surface of the vessel for each vessel geometry. Once this unique relationship is known, the complete velocity distribution at the vicinity of the inner surface can be easily calculated from the inlet gas velocity. The near-wall velocities at the outer limit of the boundary layer are substituted into the heat transfer correlation for external flow over flat plates. The final heat transfer coefficient is the area-weighted mean of all local heat transfer coefficients. The method is applied to the special case of filling with hydrogen a 70-MPa composite vessel for fuel cell vehicles.

Single and binary adsorption of proteins on ion-exchange adsorbent: The effectiveness of isothermal models.

Simultaneous and sequential adsorption equilibria of single and binary adsorption of bovine serum albumin and bovine hemoglobin on Q Sepharose FF were investigated in different buffer constituents and initial conditions. The results in simultaneous adsorption showed that both proteins underwent competitive adsorption onto the adsorbent following greatly by protein-surface interaction. Preferentially adsorbed albumin complied with the universal rule of ion-exchange adsorption whereas buffer had no marked influence on hemoglobin adsorption. Moreover, an increase in initial ratios of proteins was benefit to a growth of adsorption density. In sequential adsorption, hemoglobin had the same adsorption densities as single-component adsorption. It was attributed to the displacement of preadsorbed albumin and multiple layer adsorption of hemoglobin. Three isothermal models (i.e. extended Langmuir, steric mass-action, and statistical thermodynamic (ST) models) were introduced to describe the ion-exchange adsorption of albumin and hemoglobin mixtures. The results suggested that extended Langmuir model gave the lowest deviation in describing preferential adsorption of albumin at a given salt concentration while steric mass-action model could very well describe the salt effect in albumin adsorption. For weaker adsorbed hemoglobin, ST model was the preferred choice. In concert with breakthrough data, the research further revealed the complexity in ion-exchange adsorption of proteins.

Synthesis of Large-Scale Heat Exchanger Networks by a Monogenetic Algorithm

Abstract Synthesis of large-scale heat exchanger networks has attracted increasing attention but it is still a very difficult task because of the geometrically increasing of the design parameters to be optimized. In such cases, even long computing time were used, the result would usually not converge to the global optimum. In order to overcome this disadvantage, a monogenetic algorithm based on the optimization of sub-networks (functional groups) was proposed to improve the initial design obtained by the hybrid genetic algorithm. In this new procedure, the first search was carried out by the use of the hybrid genetic algorithm under a small population size and limited number of evolution generations so that the first design could be finished in relatively short time. Then, the sub-networks undergo recombinations and are further optimized with the hybrid genetic algorithm, in which a large population size and more evolution generations are used for the optimization of the sub-networks to ensure that the optimal solution of each sub-network can be found. An example from literature was calculated with this new method which yields a better network construction.

New Unstructured Mesh Water Quality Model for Cooling Water Biocide Discharges

A new unstructured mesh coastal water and air quality model has been developed that includes species transport, nonlinear decay, by-product formation, and mass-exchange between sea and atmosphere. The model has been programmed with a graphical user interface and is applicable to coastal seawater, lakes, and rivers. Focused on species conversion and interaction with the atmosphere, the water and air quality model follows a modular approach. It is a compatible module which simulates distributions based on fluid dynamic field data of underlying existing hydrodynamic and atmospheric simulations. Nonlinear and spline approximations of decay and growth kinetics, by-product formation, and joint sea–atmosphere simulation have been embedded. The Windows application software includes functions allowing error analysis concerning mesh and finite volume approximation. In this work, a submerged residual chlorine cooling water discharge and halogenated matter by-product formation has been simulated. An error analysis has been carried out by varying vertical meshing, time-steps and comparing results based on explicit and implicit finite volume approximation. The new model has been named 3D Simulation for Marine and Atmospheric Reactive Transport, in short 3D SMART.

Energy Integration Manager: A Workflow for Long Term Validity of Total Site Analysis and Heat Recovery Strategies

Abstract The data basis for a Total Site study is only valid for a static snapshot of the whole industry Site. Changes to single process units throughout the design phase of new industrial solutions as well as subsequent process modifications to existing plants necessitate an actualization of the Total Site analysis. Previously identified potentials to increase the energy efficiency may have become outdated or infeasible. As a first step in the development of an Energy Integration Manager, a conceptual approach for the implementation of an interface to an existing heat exchanger network (HEN) synthesis tool is proposed. Certain improvements to the HEN synthesis tool according to heuristic rules are described for enabling a suitable workflow.

New method for large-scale heat exchanger network synthesis

Abstract For the synthesis of large-scale heat exchanger networks a new method based on a hybrid genetic algorithm is proposed. It uses subnets in order to improve the resulting network structures and the calculation time. The application of the new method on an example from literature yielded a HEN structure with reduced total annual costs by 14% and a decreased calculation time by a factor of 18.

The optimal design of heat exchanger networks considering heat exchanger types

A hybrid genetic algorithm for the optimization of heat exchanger networks (HEN) considering the heat exchanger types is developed. The algorithm is based on an analytical solution of the stream temperatures. The heat capacity flow rates of hot and cold streams and the heat transfer parameter (the product of the correction factor of logarithmic mean temperature difference F, the overall heat transfer coefficient k and the heat transfer area A) of each heat exchanger in the HEN are taken as the decision variables to be optimized. With this method, the investment and utility costs can be calculated separately in a user subroutine where the specificities of heat exchangers can be easily taken into account. An example from literature is used to illustrate the procedure, and better optimization results are obtained.

EVHE – A new method for the synthesis of HEN

Abstract In this paper a new algorithm for the synthesis of cost optimal heat exchanger networks (HEN), called enhanced vertical heat exchange (EVHE), is introduced. It adopts aspects of the conventional vertical heat exchange but differs where, instead of using composite curves (CC), a new form of graphic depiction of the problems data in a temperature–enthalpy diagram is implemented. Another deviation from the conventional heuristics is to allow parallel and crossed connections of streams in the same diagram. The resulting HENs have in common that they are the solutions with a minimum number of heat exchangers (HE) for a default amount of integrated heat. Furthermore, the new method allows the option to take into account varying heat transfer coefficients by means of a substitution of the streams’ data with virtual temperatures. The EVHE algorithm proved to produce better results on problems taken from the literature.