Design and operational condition optimization of a rotary regenerative heat exchanger

Abstract

In this study, comprehensive optimization studies of rotary regenerative heat exchangers (RHEX) used in the flue gas desulphurization system are conducted. In this context, two optimization studies are taken into consideration; the first one is the optimization for the existing design by replacing the matrix elements with corrugated – undulated (CU) plates and the second one is the design and operational condition optimization to design a RHEX for the same boundary conditions utilizing CU plates. Sinusoidal pitch, inner height and the undulation angle of the undulated plate are selected as the decision variables where effectiveness, entropy generation number, and cost are treated as the objectives in the first case. For the second case, RHEX outer diameter and length, as well as the angular velocity, are added to the design variables and RHEX volume is considered to be an additional objective. Case-specific heat transfer coefficient and friction factor based on the experimental data are adapted through the thermal–hydraulic modelling of the RHEX with the effectiveness and number of transfer unit method. NSGA-II is implemented for multi-objective optimization. It is concluded that thanks to optimized CU and RHEX geometry as well as the angular velocity, RHEX effectiveness can be augmented by 92.06% with a penalty of 66.66% increase in the total cost by only replacing the existing matrix profile with CU elements. Also, minimizing the cost by 46.11%, an increase of effectiveness by 32.02% and 16.60% decrease of entropy generation number can be obtained. A new design with the same budget can be obtained by improving the effectiveness by 53.19% and reducing the entropy generation number by 18.95% in a volume which is 8.90% smaller. Similarly, a RHEX design to have approximately the same volume with the existing RHEX is possible with 50.64% increased effectiveness, 20.65% decreased entropy generation number and 23.35% reduced cost.