Configurations and pressure levels optimization of heat recovery steam generator using the genetic algorithm method based on the constructal design

In last two decades, there was a great deal of attention on the optimum design and performance improvement of the heat recovery steam generator (HRSG) units. In the present work, considering different objective functions and utilizing the constructal design method, three configurations of HRSG are compared. The design method is based on the constructal theory and optimization technique is carried out by varying the geometric design parameters and steam pressure levels for different values of the exhaust gas temperatures. Optimum conditions of HRSG are obtained with the help of the genetic algorithm under the fixed total volume constraint. For each configuration of HRSG, optimal distribution of the heat surfaces (sizes) subject to the total volume constraint are derived such that the objective function is optimum. It is shown that how the geometric and thermodynamic design variables of HRSG can be achieved, simultaneously. Features that resulted from the constructal design are the number of tubes, configurations and aspect ratios for the main sections, the tube diameters and rate of the steam production at each pressure level. The results revealed that variations in different objective functions are strongly affected by the hot gas inlet temperature. In addition, the use of several pressure levels in HRSGs causes a considerable increase in the power production, declines irreversibility in HRSGs and allows producing higher steam flow rate for all values of the inlet gas temperature. The constructal principle invoked in this paper represents that geometrical form of systems can be deduced from a single principle.